Increase in monthly contract without my consent

I am very unhappy.I just received a message saying I am getting more call time and have to pay a whole R75 more when I signed for the amount of R359 per month,without my consent now mtn garden route mall ignores my calls and the complaints manager ignore my emails.I have been with them many many years and always have been a loyal customer.I explained to them that I cannot afford to pay more they just want to force me to pay more.I have no work and I am very ill which is why I struggle to find a job.With this kind of service you will lose customers and later your store will close down.I asked them to please take it up with head office it's been 3 or 4 days and still heard nothing from them.Please never take out any contract with this company you will truly regret it!!!!!!!!!!