Christianne and Robert Shepherd died while on holiday with their father in Corfu in 2006
The parents of two children who died from carbon monoxide poisoning in Corfu have criticised Thomas Cook for not apologising to them directly.
A spokesman for the company said a letter of apology had been sent from chief executive Peter Frankhauser to Neil Shepherd and Sharon Wood.
However, Mr Shepherd and Mrs Wood said they had only been shown the letter by reporters.
Christi and Bobby Shepherd died while on holiday with their father in 2006.
In a statement, Mr Shepherd and Mrs Wood said: "We haven't had this so called letter of apology.
"Its not an apology for their wrong doing but a general offer of sympathy. It does not address the central issue that their Safety Management System failed and it does not apologise for that."
The children's parents were responding to a Mail on Sunday report that suggested Thomas Cook received £3.5m in compensation for loss of profits and other expenses.
They said they had only received around a tenth of that figure.
In a statement on Sunday, Thomas Cook said: "The Greek court, in 2010, found the deaths of Robert and Christianne were the result of unlawful action by hotel employees.
"We had the right to reclaim costs related to the trial from the hotel. The costs incurred by the company far exceed the amount that was received from the hotel."
Neil Shepherd and Sharon Wood battled to get legal aid to be represented at the inquest
The boiler was described as "decrepit" in hearings
The holiday firm had earlier said it was "shocked and deeply saddened" by the tragedy.
"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," the company added.
The children, from Horbury near Wakefield, were on holiday at the Louis Corcyra Beach Hotel with their father, Neil, and his now wife, Ruth, when they died.They were found by a chambermaid in a bungalow at the hotel.
Their father and stepmother had also become ill and were in a coma when they were found but recovered in hospital.
On Wednesday, an inquest jury returned a verdict of unlawful killing in the case and concluded that Thomas Cook had "breached its duty of care".
It found the children had been overcome by fumes from a faulty hot water boiler housed near the bungalow they were staying in.
A criminal trial had been held in Greece in 2010 following a long-campaign by the children's family.
Three people, including the manager of the Louis Corcyra Beach Hotel and two members of staff, were found guilty of manslaughter by negligence and sentenced to seven years.
Eight other people were cleared, including two Thomas Cook travel reps. The trial cleared the firm of any responsibility.