Total nightmare

On the 5th of November I contacted MFC to notify them of bank account changes and debit date that will take effect from December, they sent me the paperwork which I completed and sent back to them, on the 10th I received a confirmation that the all is received and that from December the payment will be deducted from the new account on the 15th of December. <br> <br> On the 1st of December they debited the amount from the new account, so bank details has been changed but they chose their own date, I called them and said this is wrong the documents they confirmed to be accepted clearly states the 15th, I reversed the payment, on the 15th they decducted the payment twice now saying my account is in arrears by one payment. <br> <br> And there is not one competent person that is able to assist in this. Each one tells me my account is one payment behind.