There have been other threads on this issue that might offer you insight. Each charter company is handling things differently. Some postpone the charter, with the final payment due as in the original contract; e.g., 60 days before charter.

They all seem starved for cash, so giving the best terms to fully-paid customers makes sense, unless they're not around by the new date! Would your credit card cover you in that case?

As to who cancelled, if the charter base is now closed, then maybe you could challenge your credit card deposit now. Won't make you popular, but it's your money.