Bad service

i paid off my finchoice loan and got a paid up letter on the Mon 19/01/2015 12:30 PM , requested them that the account should be closed however they never did that. i noticed that they've been debiting me R57.00 on a monthly basis ever since , some i did reverse and some i didn't. lately i have been getting calls about 10 times per day from finchoice collections telling me that i'm owing R800 and something i told about two agents that i'm not owing anything Zulfa called me on the 28/05/2015 telling me the same thing that i'm owing and in arrears , she then said but my balance is R0 then said she will call me back, someone different called me back but still said i'm owing , please note i still have a paid up letter from them. i'm so angry as they call me everyday not once and they can't resolve anything. they somwetimes call when i answer they hang up.