Charging interest on positive balances

I am currently having the worst experience closing my accounts. Standard Bank is also charging me interest for an account that was settled surely this is not right. in addition the agent(Mpho Drtsoabare call at 10:59) today was so rude at the collections help desk rudely expressing the need to tell me what my query was about. the principle is that no banking institution should charge you interest on positive amounts and on the call today he confirmed they are. this should be a chargeable offense