Cancel my contract!

I did an upgrade online for Mtn, not knowing the online application is from Mondo, there was no issues until the product arrived what she had sold me was not it, the extras she advised were not included, now when I want to cancel they are giving me a run around, first was told I can drop it off at my nearest MTN store, only to find out that it's not any mtn it is specific ones, now the other problem is that, they are not contacting me as they said my request was being escalated, I requested for a manager to contact me she never did. I'm still within the cooling off period, I want to cancel this contract Mondo/mtn Rewards is lying to MTN customers