Cell C just increase your cell phone contract every month without your consent

I signed up for 3 cell phone contracts last year December. The cost per contract was R299.00. Total R897.00. Every month the debit order from Cell C increased. Im not paying R1199.00. R302 more than what I signed up for.

These phones are for my children and I chooses contracts with specific minutes, data and min ........... How can the amounts just increase in were are in a 24 month contract???????. Ive been trying to call Cell C on 084 135 but the number has been engaged for the last 2 hours. How is that possible???????????