African bank reluctant to close my account

I had a credit account with african bank, I paid it up a month ago (21 October 2015) and received a letter stating that my account has been settled. To my surprise, last month and this morning I get still debit orders and calls from them saying that I owe them. When I called their customer service centre (***) this morning (2015-11-26 09:39) I came across people who don't know what they are supposed to do and have a very bad attitude. They hang up my calls twice! When I go to the branches to ask for my account to be closed I'm told that the only people who can help me are those who work at the customer services