Bad service at MTN

I wanted to close my account and sent them an email. They told me I would have to pay a fee, I said fine just close it. More than a month went by without any further news. Then a new MTN shop opened in my area, so I went there to close the account. I had to go back three times and wait a month before they assured me that the account is now closed and everything is fine. Now I'm getting contacted by their credit bureau because according to them the account is in arrears