More Pathetic Service From Cell C

I had a Cell C contract which I cancelled about 9 months ago. It was a while ago so I do not recall the exact date. As per the call centre agent I spoke to they advised that I should do a cash deposit for the amount she stated with my cell number as the reference which is what I did. I made a point of asking if I need to send the proof of payment and I was assured that there was no need. Now I'm getting calls at my place of work advising that I owe Cell C over a R1000. The lady that called said she could not help me and I'm giving her an attitude. Can Cell c not understand my frustration?! I then asked her to get a supervisor to call me and she said there is no supervisor all she could do was put a note on the system. Then she says I need to call the call centre, which I find shocking! To say the least! I now need to fix an error made by Cell C. Needless to say if I cancelled my contract it is logical to assume I do not have a Cell c number to call from! The lady also says to me she sees a cash payment done on the system but she doesn't know why?! Clearly not the brightest tool in the shed! I am extremely frustrated with these calls! I will expect some decent feedback soon!