The phone rang incessantly, but nobody answered. After what seemed to be the 20th attempt, a woman picked up the phone and said something in Russian.

"Sergei, Malta?" Karl Bonaci asked her, as his wife, Romina, clasped her hands together hoping she would get to speak to the boy she took care of for five years before he was taken back to an orphanage in the Russian town of Bezhetsk last January.

There was some shuffling until someone else returned to the phone, again speaking in Russian.

"Sergei Federov. Papà da Malta," Mr Bonaci shouted down the phone, as the well-known actor took a break from an interview with The Sunday Times.

It is a regular episode at the Bonaci home, with the couple trying for hours to get through to the boy they now love as their own. Many times the phone remains unanswered; on other days the language barrier is impenetrable.

Sergei was brought to Malta in December 2003 by the International Charity Society (ICS), originally for a month's holiday.

The boy, who was seven at the time, was painfully thin and unable to make eye contact. Ms Bonaci thought he was disabled, but doctors said he was just traumatised.

"I was shocked when I saw him," Ms Bonaci said, as she removed Sergei's school uniform from the wardrobe, where his clothes are still hanging and his schoolbag is full of his neatly-covered copybooks.

But he started making good progress and after the month was up, the couple decided to try and extend his stay. The progress was unbelievable. When he arrived in Malta he could not even string a sentence together in Russian. B ut he soon started speaking Maltese.

A video the couple have saved on both their mobile phones shows Sergei, the day before he left Malta last January, speaking in fluent Maltese, telling his 'parents' he loves them.

"I love you all. I'm going. See you," he says, before blowing a kiss at Mr Bonaci, who was filming him.

In September 2008, the Bonacis were told Sergei needed to go to Russia "for some documents, and would be coming back". He returned in December, but the couple were told he had to return to Russia in January.

ICS director Irina Malikova said that if the authorities went to the orphanage and did not find Sergei, there could be problems, Ms Bonaci explained.

"Why did they leave him here for five years only to take him back to an orphanage?" her husband said. "If he was going back to his family, we would be willing to help them. But why take him away from a family who loves him to put him in an orphanage?" Ms Bonaci asked.

The couple had even started the process of adoption before Sergei was taken away, but this stalled since they do not even know his whereabouts.

Recently they were told Sergei was in hospital. They finally managed to track down the number, before speaking to him. But what he said was incomprehensible.

"He said he had a tummy ache, but then said he was going to eat. It just didn't add up," Ms Bonaci said. They do not know the hospital's location, or what sort of treatment he is receiving. The shuffling could still be heard on the other end of the line as Mr Bonaci patiently waited for someone to pick up the phone. "Hello," a girl finally said.

She is one of the children who, like Sergei, spent years in Malta and can speak Maltese after being brought to the island by the ICS, originally for a holiday. But they have been taken back to Russia, leaving many heartbroken families. "Sergei's in hospital," the girl said, throwing the couple into even deeper despair.

"What is wrong with him? He's been in hospital for way too long. I just hope he was not sent to some mental institution," Ms Bonaci said, hugging the Mickey Mouse soft toy that Sergei loved as tears streamed down her cheeks. Her husband's voice trembled as he asked the girl how she was faring. "I'm OK," she said, although when prompted she admitted the food was not good and that she wants to return. "My biggest disappointment is that he wanted spare ribs at a restaurant and we did not go before he left," Mr Bonaci said.

Children taken back following tragic accident - Malikova

According to Ms Malikova, the children from the orphanage in Bezhetsk were taken back to Russia after Maxim Vorobyev, an orphan who had been in Malta for seven years, drowned earlier this year. The boy, who was being taken care of by a family from Valletta, disappeared on February 25 and was found dead 10 days later.

When it was pointed out to Ms Malikova that Sergei was taken back to Russia before Maxim went missing, she said this was because the Bonacis had started the process to adopt him, and the child had to be in Russia for the process to start. "When they adopt the child, he will come back and the Russian authorities have promised to help," she said. However, she does not know what happened to Sergei.

Asked why Sergei and a few other children, including Maxim's siblings Alessia and Artem, had spent such a long time in Malta, Ms Malikova said the orphanage's director, who was the children's legal guardian, had granted permission.

Mr Bonaci had claimed he paid thousands of euros to Ms Malikova over the years. However, she said the money was meant to cover the children's travel expenses. When it was pointed out that Mr Bonaci said he was asked for money to cover notarial fees, Ms Malikova said this was normal practice since it was expensive to bring children over from Russia.

The orphans' organisation

The ICS was formed in 1998 to bring Russian orphans to Malta for a holiday with local families.

But there have been problems along the way, including the resignation of its president, George Hyzler, in 2000 because he wanted to see audited accounts.

Host families had voiced concern that the children were not orphans, but had come to Malta for a paid holiday. ICS had said the children were not always orphans, but came from families in need and from charitable institutions.

In 2002, the Russian Embassy in Malta told a local newspaper that the society was not credible enough.