Cell C trying to **** me on a closed and paid up contract!!!

Cell C sends MBD to call me on regarding a closed and paid up contract. I contacted Cell C and everyone I spoke with keeps telling me " according to what I see on the system, you do not owe Cell C anything" I then ask for assistance regarding MBD because they always call and say it is on behalf of Cell C. Cell C tells me my query is not Cell C related!! Njani??? NXA!!!! ANDIDIKWE8