Paid my past due payments for EA Access, but account still suspended?

You would need to contact xbox support billing section to settle overdue payments

1-800-4my-xbox if you're in the US/Canada or http://support.xbox.com/contact-us

Does the message say "there was an error on our end and waiting a bit might help"

This can happen if you have a past due balance on a subscription for instance if you paid for a subscription with a debit/credit card and did not turn off the auto renew and when MS tried to renew your subscription it did not go through for whatever reason.
MS still allows the subscription to run while trying to get payment for the subscription. They will then suspend the service after not receiving payment after a month and consider the payment for that month past due. While there is a past due payment you will
not be able to put in a pre paid code and will get the above message.

With that being said to check you subscriptions to see if this might be the issue you would sign into your account at account.microsoft.com/services and any subscription that is past due will show up as red on that page and give you an option to take care
of it.

Unfortunately past due subscriptions can not be paid with Microsoft account/Gift card balance.

A different credit/debit card than what was used on the past due subscription in order to clear up the past due payment.

If it was through Paypal and it declined that one is hard to know for sure. It may be okay through Xbox but Paypal will have a balance due or Xbox may show as past due until that is paid. You may not get suspended for points not going through but they
can lock your account for non payment so you cannot buy anything else until that is resolved.

first do not reply to old threads, second you will have to speak to billing once you get the payment past due paid THEN you can redeem the pre pay card. you had a payment that did not go through (expired card or lack of funds on said card) that is why
you got suspended, once that balance is paid it will be lifted.