Thanks to everyone who responded. Indeed the issue is that the account is now closed, As I had booked the flights 4 months ago I didn't think about the option to cancel the flights nor did I foresee I would need to close this account.
I can ask about the check, not sure French banks can process foreign checks, at least the check would be in euros. I'll ask my old bank just in case there's something they can do.
Thanks so much for your help, I'm relieved to know they can't just keep my money...