Extremely frustrated

I've been with Vodacom for more than 20 years. But I'm getting tired of airtime disappearing. I've checked for subscriptions, there is nothing. So where is my airtime going? And also in the last year my contracts went up a few times. What is the use of signing a contract if they can change the price? Every little bit that I have to pay extra is difficult for me. I'm paying R100 more than last time this year. I know prices go up, but they can at least increase the price on the new contract. After all, you take out a contract that suits your budget.