Cancellation of Cellphone contract

during Sept 2017 I received a call from Summer Sun Trading offering me an upgrade on my existing contract with MTN. I was not informed that this was a 36month contract. I was promised delivery of the new phone within 7 days. After 2 weeks the phone was still not delivered. I phoned Summer Sun Trading asking them to cancel the contract but the debit order went through in any case. Since then I have been phoning weekly and everytime I get a different excuse. 3 weeks ago I sent an e-mail to MTN after someone gave me the address of the complaints department. I am still waiting for an answer. Could you please help.