Mtn incorrect billing terms, *****

I have taken a 24 month contract on January 2020 which should end in January 2022, my contract is now ending in August 2022 which is incorrect, according to your instore manager, there was a system change that mtn has done which has caused this, after numerous attempts to resolve this nothing has been done to correct this, that is an extra 8 months that I must pay extra cost for no reason, please correct your problem