Seperate contracts

I have a contract with cell c that i took out in 2013 after over billing me im now being told that the contract was only taken in 2014 and that i have months remaining. Wheneva you take a contract over the phone you dont receive a printed contract so I dont have proof. The only proof they have is there systems that they ammend wheneva they feel like thats why ive been paying for 2 lines for the past 7 months. My problem now is I have 2 contracts with Cellc that Ive taken individualy and now need to do a sim swop on my one nr that ive lost. Im unable to get a sim swop due to this contract I refuse to pay which is finished according to my knowledge. How can they refuse to do my sim swop if my accountbis up to date? I cant pay for a line that is done that has been cancelled in Aug 2015 and reinstated again just because they have the power to ammend the systems as they feel. This is totally **** and is **********. Ive even consulted with Icasa but it seems the consumer is always going to be the loser and just gona have to pay up.