The 29-year-old Saracens player, who has 46 caps for his country, suffered a serious Achilles injury in 2001 which sidelined him for over six months.
He made a successful return to the French national team during the RBS 6 Nations last year and was poised to make the trip to Australia for the World Cup last autumn but he was replaced by uncapped Brian Liebenberg for the competition.
"I was not expecting to be left out," Castaignede said. "It was the biggest disappointment of my career, far more painful than my injury.
"I did not get any explanations. I don't blame Bernard Laporte, he had choices to make.
"But he had told me before the summer tour that he would need me and in the end he chose Liebenberg who had never played for France.
"I would have gone to that World Cup, even as a substitute."
Castaignede thinks Laporte, who decided to stay on as coach for the current RBS 6 Nations tournament after his side reached the semi-finals in Australia, is unlikely to hand him a way back into the international fold.
"I have not heard back from the coach since the World Cup even though I still want to play again with Les Bleus," he added.
"But I feel that he is not interested in me anymore.
"No one came to visit me, neither Laporte nor his assistants, no one called my coach.
"I am not asking anything and I keep working but the French team is not something I have forgotten for good."
Although he is not part of the 2004 RBS 6 Nations campaign, Castaignede has been watching his national side's performances and is convinced they can dethrone England.
"For me France must clinch the Grand Slam," he said. "They have a good schedule, the only thing is to beat the English."