the story of a loyal client being abused

I am a life long client of mtn, been with them for over 20 years absolutely love their network. But of late I have receive the worst kind of service imaginable i signed a contract with them verbal of course and they ****. Promised me 25G but delivered 15G. They suppose to charge me R 179.00 but they charge R 327-62 I have been on the line with them 3 hours, no resolution they are doing what I call client abuse to me. Nobody takes any responsibility one of their supervisors tells me its 15G this month it will be 25G next month imagine, what nonsense. In this day and age 36 days into the contract I want to cancel because they can't deliver and they want to charge me R662.37 cancelation fee, its a sim only contract no device. I demanded to speak to a manager at cancelation and guess what they not allowed to speak to me "they will call me later" CLIENT ABUSE I call it I am a victim here somebody any body help