My credit card is in use to an acccount that is...

Question

Hello! I just tried to switch my Pay pal account to use my AMEX card as I no longer have my visa. However Pay Pal said that my AMEX card is already in use to an existing Pay Pal account. I do not know who's or what account. But I want to cancel my AMEX or whatever account it is connected to so that I can use that card on my account.