Harassments and failure to honour debit order arrangement

This is really frustrating, I am getting 4 to 6 calls a day (If this is not harassment then I don't know what is) about when i will be paying my account. I have a standing debit order with you but you decided not to debit my account in Nov and Dec. And now i have your debt collectors calling me as if i don't have a debit order arrangement with you. i asked the lady who called to give me a detailed report as to why you could not debit my account, what was the error from the bank because there are funds in my account. now this will show on my credit profile as a late payment, when you decided not to honor the debit order agreement that we have. I seriously don't know anymore