Disappointed in their service

I did an early upgrade with cell c last year January meaning my contract on this package must end in January 2016 but unfortunately not according to Cell C. I am being told my contract will be ending in April instead meaning My contract will now be over 24 months and how is that possible????. As far as I know I entered into a 24 month contract and not 27 months contract. All the service providers count the months from when you did your last upgrade not this stupid network.no wonder someone put a bill board about the pathetic service