Fnb refusing to assist, doesn't want my money

Over a year ago I went to Fnb to close my accounts because I had only zero balances, but 2 weeks later without warning, 6000 was added back onto my zero balance revolving loan. Turns out they made a mistake and deducted the last few payments from someone else's account and corrected when I came in to close mine. When I went back only the manager was able to look at me and speak to me, but the consultant who didn't even acknowledge that I exist and was sitting in front of him, still working at Grassy Park FNB now. My problem now is, I want to make an arrangement with FNB to switch my salary back to them and slowly start repaying the debt that they messed up on, but they are refusing to assist me on the FNB chat app or answer when I call. I even asked them to call me and they said they can't.