If it is not possible for them to debit your account, a so-called return debit occurs. In this case, you will receive a corresponding payment reminder by email with the request to transfer the outstanding amount (invoice amount plus flat fee) to their account.
If you suspect an error with your open items, please contact their accounting team.
If, after repeated reminders, no payment has been received or they have not received any feedback, they are unfortunately forced to block your account and forward the process to a debt collection company or their lawyers for further processing.