unreasonable and forcibly increase

I signed the cellphone contract R399/Month with Cell C near 2 years. I just realize that the contract price from R399/Month increase to R419/Month 3 month ago. It is irrational and rude. How can Cell C increase the monthly contract fees during the contract period and the customer can't have any choice? I phoned Cell C customer service to complain and a lady reply me that Cell C have the rights to increase any amount during the contract period and it is write in the terms and condition which we didn't receive when we sign the contract. I have used MTN for over 15 years and never happen to increase the month fee during the contract period. I will tell all my friends to use Cell C and never and ever to sign the contract with Cell C again under this condition and service. Because they are deceive the consumers.