Customer care service nonexistent

Initially I was very happy about the app. But I’ve been trying to contact the app developer for a problem I’ve been having for months now without any success. I have no possibility to delete the registered payment methods, it seems it can be done only by them. I need to delete one of the two iban codes I’ve inserted because in the format they appear on the app there’s no way for me to recognize the right, current one, and reimbursements have now been made several times to the wrong account.