Being debited after account has been paid up.

My account was paid up at the end of Feb. End of March I was debited again not for the full installment I had been paying. I have been calling the Call centre since last Thursday. The consultants have been helpful. however my account still shows a balance and I am waiting for a paid up letter since last Thursday. I have spoken to different consultants each time I called, however this query is still not resolved almost a week later. I want my account closed.