The creditor number is incorrect or has been changed without a change being communicated via the pain008.
The creditor accounting package may have created the wrong number due to a technical error. It is also possible that in the context of a B2B mandate, a change ("amendment") of the creditor number has not been communicated.
Correct the creditor number or conclude a new mandate if it is correct. Finally, it is advised to check with your bank or Sepa Direct Debit Expert whether all parameters in your instructions to the bank are correct.