Terrible signal and no support

I have been an MTN customer since 1996! Over the last 4 years I have called MTN on a regular basis to inquire as to why I cannot get decent signal in my home / office area. I live in the roodepoort area. I own my own business and need to be in contact. My calls don't connect, they get cut, the call quality is ********** and I've tried everything. I often have no signal at all in most places in JHB. I have called the call centre, sent emails, spoken to MTN coverage consultants, and to date have received no explanation as to why I cannot get what I am paying for. They have 3G, 4G and everything in-between, but try making a decent call and it's useless. On 1 day I dropped 10 calls, and the other 6 had such bad quality! I'm concerned that MTN is actually in trouble with over-promising and under delivering. What is it that they are not telling us about their network? Is is about to actually collapse? Can it not handle the load? I have had no help at all other than a booster on my premises which only works when there's signal! Am I in my rights to cancel my 4 contracts and go to a competitor? As they seem to not be able to honour their side of the contract and give me signal & service!