Action Required: Irregular activity in your AWS account.

I have a problem, AWS reported suspicious activity and sent me a bill for $4200. I have never used AWS since I signed up 2 years ago. Yesterday, I spent the day with the help desk to delete the log groups, models etc... My bill is blocked because my credit card is no longer valid. The call center told me to put my new valid card which will be charged $4200 and then recredited by them. But I think it's risky. I want to leave my expired card which prevents a charge. I don't know who to do about this bill. (AWS recognizes that my account has been hacked)