WHY DO I EVEN HAVE A CONTRACT

Why do I even have a contract with MTN??? I signed up for a contract of x amount per month only to receive an sms saying that I am in ARREARS. Upon querying this I was told my bill went up by R10, I asked why and was told CLAUSE 19 of your contract. Your OWN employee's don't even know about it. it says that you MTN can alter the contract as YOU please, well, thanx for NOTHING. R10 may not be a lot to YOU but how much money are you making out of the MILLIONS of customer's you have. I BUDGET for my account not a cent more or a cent less. Maybe it would be a good idea to switch over to Cell C as they advertise it won't cost me a cent and I am GUARANTEED to pay the SET amount for 24MONTHS. I ALSO haven't received a BILL for the last FOUR months now. Amazing how quick you are to suspend someone's account BUT get NO accounts. My contract is NOT a contract anymore. I guess a lot of customer's will be either be changing networks or going pre-paid OR take the CHEAPEST contract which means EITHER way, MTN will loose out financially, just like I and MANY other customer's have