MTN just signed up a new contract for me without my consent hitch is way too expensive as I am a Pensioner

I had many contract with MTN and was happy with them however their service has gone down to the dogs. My contract I took out with them had expired and they took it upon themselves to give me a new contract without devising me. My contract we R140 for 40 gigs. They gave me a new contract after my two years es up for R530pm for the same amount of data without advising me. I paid the first month no went to MTN at Clearwater mall to have it cancelled as I did not sign for that contract. I was debited and had the debit returned. No they have handed me over to their Lawyers who continue calling me. I will not pay and refuse to even listen to them cause I have spoken to so many people explaining but it falls on deaf hears. I even called their call centre. I m sick and tired of their calls cause I m not going to explain again to another person from MTN. I don’t know what has happened to them cause the service is pathetic.