Travel firm Thomas Cook has issued an apology to the parents of Christianne and Robert Shepherd who died from carbon monoxide poisoning in Corfu in 2006.
Peter Frankhauser, the chief executive of Thomas Cook, sent a letter of apology to the parents, although Sharon Wood and Neil Shepherd said that they had not received any such correspondence.
It has also been reported that the company got £3.5 million in compensation for the deaths, but Mr Shepherd and Ms Wood said they only received about a tenth of that figure.
At a trial in Greece in 2010, the holiday firm were found not responsible for the deaths of the children and awarded an interim payment of £1 million by the court.
Thomas Cook said: it was "shocked and deeply saddened" by the deaths.
It added: "Thomas Cook recognises that the pain caused by this terrible accident will never go away and must be still very hard for friends and family to bear."
In a comment, Mr Shepherd said: "We all loved the idea of a bungalow because it looked out on to the sea and our children Christi and Bobby could run in and out to the gardens.
"We thought it would be a wonderful family holiday with happy memories. Instead it was to be the children's last days on this earth."
Three people were found guilty over the deaths at a criminal trial in Corfu in 2010, including the manager of the hotel and two members of staff.
