Telkom billing me incorrectly results in my contract being extended by 3 months

I took out the contract on 23-06-2017. Telkom then proceeded to then bill me incorrectly. They were charging me R249 a month instead of R199 a month as per the contract, IT TOOK ME MONTHS TO SORT THIS OUT. It must have been corrected around September 2017. Now, 24 months later when the contract has 'come to and end' and i want to cancel it, they wont allow me and want to charge a penalty for early cancellation?? They are telling me the contract was taken out in September 2017. My contract clearly states 23 June 2017. The two people that I have dealt with have been unhelpful, they have **** about never receiving any of my emails with the contract attached, they have apparently 'tried to call' me. I have received no feedback from them whatsoever. The contract was taken out 23 June 2017 and should have come to an end on 23 June 2019.