Worst network provder. I regret being their customer for over 10 years

I am shocked after a call I made to MTN contract line today. I have a contract with MTN and have just been informed that they will NO LONGER be able to top up my number with minutes upon my request. Reason being they have implemented changes which include that I will be charged R1.99 cents per minute for calls as a result of the package I'm in. Fair enough I guess they are allowed to chop and change their services as they please. But why must I/we be affected by such changes if I/we have already signed a contract with them???? I don't get it and will never get it. No they've pushed me too far. I almost cancelled this contract because MTN alleged that I owed R400 000 and mind you I don't have a business. On the other hand they were also charging me for features I never had on my contract. This issue took more than 6 months to be resolved, I had to bare a situation where my line would be suspended almost on a weekly basis as a result of their negligence. I'm seriously fed up with this network provider I'm canceling my contract with immediate effect.