Contract cancelation

I app**** for BlackFriday Promo online for router n 100Gig for r299, I ddnt get reply i then went to MTN West Street, lady said 100Gig promo is SoldOut, I took contract, I got email from MTN replying to my online 100gig order saying it still available, I went bk to store to cancell contract following day, but lady refused telling me her manager said I must call 135 to cancell it but call centre told me to Go bk to store, Der giving me runaround so 7days return policy wl lapse