Desperately need to cancel my contract, please help.

Signed up for the contract on the 9 Jan 2018, days later phone overheats and screen becomes blurred. Took to the Gandhi Sq. and told my warranty is void because i use 3rd party sim card, of which phone was activated with it by the consultant . It was a long debated issue to have the phone booked (24/01/2018) in for repairs because of no warranty. I been waiting forever and not annoyed with the after care service from your Gandhi Sq. outlet and terribly regret the day I signed up for the contract, more so with Vodacom