Pay back the money

My mother has a home loan with Nedbank. She got billed twice this month, they made a double debit. When she called to enquire, they said that she hadn't paid for November 2014 and January 2015.. That was a load of Bull, because we had proof of payment for both those months. They said we should fax them through, we did that. I even scanned the documents and emailed them. The branch manager said he'd follow up, from last Friday already. It's Tuesday, still nothing. My mother called him and he said that he hadn't heard anything from the head office. How hard can it be to reverse a transaction that was made by them?? And yet when you owe them, they send out their virtual search teams to attack your bank account! How difficult can it be to give the money back?? PAY BACK THE MONEY!!!