Incorrect amount debited

I sent Thomas Revonne an email on the 28th of January to amend my banking details as I swictched to a different bank. He first said hes unable to amend them for the following month which is february but he wil do so for the month of March meaning I will have to make a manual payment for feb. Today 2015-02-27 i get a message from my bank that R1 443.00 has been debited from my account to ADT and my REQUIRED MONTHLY INSTALLMENT is R300.00-. I called their offices and I could not get ahold of this THOMAS REVONNE person or any credit manager. I WANT ANSWERS NOW!!!