Unauthorized Deduction

My mom has vehicle finance with MFC, which I currently pay by transferring money into her account for the debit order. We wanted to update it, so that my bank details reflect on the finance, and the debit order comes directly off my account. She sent an email and requested the change of bank details, and they rep**** with forms and the process, whereby we need to provide my bank statement, letter of authority etc. After this there was no communication, and then I get an sms with the debit coming off my account, after I had transferred money for this debit order into my mom's account. The response I get now, is that they cannot help me however, they were more than happy to deduct money from me. On top of this, when I tried to call them their systems were suddenly offline. What poor, poor service this people have provided. I wish it was easy to move vehicle finance to another bank.