Cant wait to cancel contracts

I called into the call centre of MTN was helped very nicely by a lady who advised me that one of my contracts are due for upgrade soon, I advised her I am needing to find out how to cancel that contract, as I know you cannot phone to get into retentions, she kindly sent an email to them, I received an automatic response stating 24 hours to get a response ********, the nonsense of them saying they will get back to you is a lie, the SLA of mtn as a whole has failed and I just upgraded another phone and regret ever doing it, I need to find out how I can return my upgraded phone which is just under a month and have both contracts cancelled, as I would rather be stuck with a broken phone than with a pathetic service provider!!!!