Maybe something went wrong with your payment and the amount could not be debited. In this case, you will see a note in your profile about the existing payment arrears and you should also have already received a payment reminder by e-mail to your stored e-mail address.
Within the first 20 days you can still settle the account directly via your profile in the user menu under "Payment admin". Simply select one of the payment methods offered there and follow the instructions.
After the 20 days have expired, you can only pay the arrears by bank transfer to the bank account specified in the payment reminder you received.