Contract Term date incorrect

I have been trying to get my contract term date corrected for a year now. In Feb 2017 I upgraded my line through Vodacom Online (Worst mistake of my life). the handset when delivered was faulty and I returned it as per their process. It took them two months to acknowledge the return and to do a reversal.

in April, I then upgraded the same line in store (as I will NEVER use Vodacom online again) and everything was fine UNTIL I saw a few days later that my contract term was not 2, but 4 years (Contract end date 2021)

I phoned the whole world and been sent from pillar to post to fix the problem. I called Upgrades, Vodacom online, After sales, Cancellations and each time they refer me back to another area with no joy. its been a year now and I don't know who CAN help me fix it.