Unapproved changes and charges

I had a contract with MTN which I have been renewing for several years. MTN has always contacted me previously regarding renewal of my contract however this year I received no communication (sms/email/phone) and my contract was automatically changed to a new deal without my approval. This is an exorbitant contract not fitting my needs whatsoever and is over four times the cost of my original contract. When contacted MTN staff tell me I agreed to this clause in my terms and conditions, and that it is irrelevant that this has not happened previously. I am absolutely enraged by this blatant manipulation from MTN. They will not let me cancel the contract while I dispute these charges. I will encourage anyone I know and also do not know to never make use of MTN services