Service provider with no service provided

I would not suggest MTN South Africa to anyone, I have been a client of theirs for more than twelve years and the last 5 months I have had my service suspended without any prior warning every month despite me paying extra on my account every month. Not only that, the last two months they have blocked my service without warning twice a month. Not only do they blame me for not paying my account (which their accounting department did not allocate, despite me sending my proof of payment several times to several different employees), but they are now delivering no service whatsoever and is endangering the safety of my family since I find out I've been suspended when I try to make an urgent call. In Februaty I could not call a doctor since they had suspended my service without any prior warning. When I asked them why they suspend my service when I've paid in full, they inform me that it's either "technical difficulties" or late payments (I need to have my payment made by the 10th of every month, but they block me on the first, despite my payment being made before the end of the previous month). They are endangering the safety of me and my family, costing me income when I can't reach my clients and are wasting my time since I have to make sure their accounting department actually allocate the payments I've sent proof of several times. And now that I am trying to cancel my account because of their breech of contract for not offering me the services I am paying for, they still expect me to pay the cancellation fee. I will never make use of their services after these last 5 months.