American Express Issued Me A Check 12 Years Ago That I Never Cashed, Do They Still Owe Me That Money?

Apologies if this seems too trivial, hoping someone just might know the answer.

I closed my account with American Express in 2013 and they sent me a check (just over $500) to settle the remainder of my balance. The check was misplaced, then I forgot about it, and only just now found it in my archive.

I called AmEx to ask for a new check and during my first call they quickly processed it and assured me a new check was in the mail. Instead, I got a letter stating that the account balance was zero and therefore they could not process my request. After I called the second time, they took the position that since I didn’t cash the check during those 90 days that it was valid for, AmEx no longer owed me any money. Are they right?

Thank you very much in advance!