Cell C claims I did not finish paying my contract

I paid the my cell phone account finished after I was handed over as soon I finished paying the account cell c sent me my statement showing that I am sitting on 0 balance owing to them, on the very same day a different debt collector called me and told me they need to make arrangements for me to pay my cell c account, when I advised them that I paid my debt finish they say I must take it up with cell c, when I contact cell c they say they cant advise on the account because it was handed over. So I am being pushed from one place to another and I am now left with a bad credit record. If anyone can assist in getting this sorted.