Contract Cancellation

I went to mtn for a new contract phone ans i app**** for 24 months but the agent made it 36 months. I decided that i cannot afford to pay for 36 months and returned back the phone to the store on the 29 january. Till today the contract is not cancelled and my old mtn number blocked because of non payment and i keep on receiving emails that contract is on arrears. MTN is ruining my credit record. 3 weeks back i got a call from Portia calling from the cancellation department and she requested me to send the cancellation form and i did but still nothing has been done. I regret the day i went to mtn for a contract. They are so unprofessional and they dont care about their customers. From 29 january till today they are failing to cancel their contract where else they took back the phone. I hate mtn😡😡😡am even tired of sending follow up emails because i don't get any respond. Bad customer service!!!!!!!!!!!!!