Service non existing

I’ve been a loyal customer for many years only to find out that my last month account was debited from a banking account that’s not mine. The problem is I didn’t give them the approval or ask for the banking account to change. Now I have for the last five days tried to sort this out. I have been promised by more than five people every day they will get back to me without success. All empty promises. I sit on the phone for hours with no success and they don’t want or don’t give you senior people to talk to. I’m fed up and have cancelled all my contracts and stopped my debit orders. Let’s see how quick they will react now.