How do i found out which credit card is used to charge my icloud storage

You could look on the purchases list or statement(s) from your credit card provider(s) for the correct iCloud amount paid to Apple.

or

It would most likely be the payment method at the top of the list in your Apple ID Account.

(You can change the order of your payment methods if you wish.)

You could check online:

Apple ID Log-in:

https://appleid.apple.com/

or check here to change the order of your payment methods

Change, add, or remove Apple ID payment methods - Apple Support

All the best :-)