Unacceptable payments without service

Over two years back I was phoned by Motorite /Wesbank consultant and I was advised to only join their service plan I will be paying R250 per month for 2 years, then I received and sms that it will expire on the 31 of January 2018 but suddenly they still deduct R350 of they only told me about R250 telephonically I never mind about them adding R100 on top of R250 that I was told about telephonically and documents were sent with an addition of R100 and yet their service plan doesn't cover everything maybe they didn't advise me about it because it was my first time buying a car so everyone takes chances to someone who knows nothing but what worries me is that they said I will continue paying this money until I finish paying my instalment for my car that's so ridiculous they are really knocking me how do I pay for service that is not going to be rendered to me??