I need to change my payment method, but my wife set up account on HER account, but has since passed away!

My wife set up an Apple iCloud account, using one of her credit cards. She has since passed away (died) and I need to change the credit card paying the iCloud account, but do not have her credentials or the iPhone she used to set the account up with. I can, of course just cancel the card, as I must, but whatever data is in the cloud account will be lost.