Double Debits and no Accountability.

Very frustrated with MFC and their collections department I changed banks to Nedbank because my car is financed with MFC, making my debits easier and reducing admin. I called on the 8th of October to query why my account was double debited from the finance house, and MFC said that they couldn't locate the second debit order After a week of fighting with them, they finally advised that there was an issue on their side, and the second debit order shows unpaid, but the money was taken from my account. They are saying they can't refund my account, although they made a mistake. They also debited my account with nearly a 1k more than my agreed installment amount, and they are unable to explain the reason for that. Can someone please advise if it's just me, or has anyone else experienced this with Nedbank/MFC