Price Increase on Fixed two year Contracts

MTN ,Have app**** a tariff increase of 9 % on a fixed term contract and the monthly subscription fee has increased from R99.00 too R109.01 .The contract signed on 2014 -10 -24 for a monthly Subscription of R99.00 is not being upheld .The terms and agreement has been breached and is not valid any more .A letter from customer Services informed myself that increases were from R10 to R24 depending the type of package .How can fixed contracts be adapted at a stroke of a pen without any communication what so ever .This a breech of contract .<br> <br> Concerned Customer <br>