Mtn contact cancelation and billing

Hi, im very disappointed in mtn service, i have been a customer for over 10 years and its always been a battle, recently i have tried to cancel my contact due to the month to month billing being ridiculous, and its on a month to month billing as they do not have stock of the device i want, i would like a refund for the amount over charged and please cancel my contract, i dont have the time to wait 20 to 30 minutes to speak to people that cant assist me.