Cannot upgrade my contract

I have a home bundle that I spend a certain amount of money on every month. It includes my home line and internet bundle. I want to spend more and Telkom doesn't want me to they say I have to buy out my contract so I can spend more every month. I have never heard of a company not wanting there clients to upgrade and spend more money if they are capable of it. I can understand being charged if I downgrade absolutely because now you would be spending less. But to say I have to pay up the balance/remainder of my contract so I can spend more every month makes absolutely no sense! The Internet is just no longer enough for my household and would like to increase/upgrade my contract with them.