Contract error NOT being rectified!!!

I have called and called and called! Nothing is being done to correct an error made by Vodacom! I am told the error has been corrected but it hasn't! In April 2018 I took over my Vodacom contract from my dad (change of ownership) and upgraded soon after. I signed a 24 month contract. I should be up for an upgrade in August 2020 the latest but Vodacom is telling me my next upgrade is on the 22 November 2021!!! That is around a 43 month contract!!! The phone will be paid off by August 2020 but I must keep paying?! That is *******!!! I don't even want to upgrade next year but I definitely don't want to keep paying for a phone that WILL be paid off. I want to end my contract with Vodacom next year and NOT in 2021!!! I called the call centre twice and the incidences were logged. They told me to call the Vodacom store where the change of ownership happened as that is where the error occurred. I did this 3 times, was told the incident was sorted out but when checking when the upgrade is, on several occasions it is clear the issue hasn't been rectified. I again have called the Vodacom store but no-one wants to help or calls me back! This is unacceptable!!! I want this error rectified!!!!