***** within Telkom stores

In 2019 I did an upgrade at the Telkom branch in Adderley Street Cape Town. The agent who assisted me explained to me that the deal I want is a 24 Month Contract for R750. The deal was a Router, 40 gigs data day and Night plus a Samsung smart Television. I agreed and signed the contract stating 24 months which I have the actual contract still. 1 year later upon using the Telkom app I saw that their system showed 36 months. For the past year I've been struggling to have it sorted yet each time I'm told I'm liable for the mistake. Please tell me how the heck I am liable for a Telkom agent who mislead me, manipulated the system and committed *****?