Pure theft via debit

I signed up for a Mofaya 5 gig special in June 2017. The special was advertised for R199 on a 24 month contract. Vodacom consistently charges me R209 every month and when I queried this with the contracts department, they couldn't explain why the bill changed from the amount on the contract. It is pure theft on their part. *****ing from customers when the contract clearly stipulates a specific amount and they debit a higher amount with no plausible reason. Unacceptable