*********** cell c staff unable to assist!

I bought a cellphone from cell C in 2015I have been requesting for my contract from them since late 2017 early 2018 for they claim that there's an outstanding amount that I owe them but I know very well that I paid them all that is due to them now the case has been refer to MBD inc. but whenever they give me a call I always ask for the contract for me to see if I did request for them to extend the contract but they keep failing to do so for they keep telling me that they do have all the documents how can they expect me to pay them if I don't have the contract to see if I "agreed" to the extension of the contract and MBD inc they only thing that they keep telling me is that they do not have the contract I fail to understand how can they take a case and not request for all the necessary documents!