Does price change affect your set contract price

Hi there just like to share my experience with telkom.. I have 2 existing contracts with them.. For the past 2 months I've been charged more now for my contracts with no notifications or reason only to phone the call center and be told there is a price increase and nothing can be done.. So how does a contract price change cause of a price increase.. Please assist telkom as there is no joy with your customer care and do explain how can a contract price change... If so you have lost a loyal customer cause that does not make sense a contract is something that is set and cannot change