How can I add a Credit Card,when it seem"you have reached the maximum number of credit cards allowed on an account"?

You need to contact the support to reset the counter

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CONTACT FORM

You can also fill a contact form from your account Once logged in, from the account panel go to My Profile → Contact Form (the subject are limited) and fill out the form and someone will email you back.

You're talking about the credit cards in your "Payment methods" right? If so, you can just delete the old one(s) and add a new one.

Is there a reason that you need so many at the same time? If not, then you can just remove one that you no longer use.

Have you found a solution for this in the end?