bad service

I took out a contract with nestar late last year (when I was taking delivery of my car), I called them after the unit was fitted to find out how it works and the benefits of the system. In that same call I asked them about the costs of the system and I was told my instalment will be R149 or something. To my surprise I got a debit order of R1241.53 when I called the to find out why, their consultants put me on hold for long and no was able to explain to me why, until I decided to cancel the contract. I fear that their incompetence in such a small matter like billing left a bad taste in my mouth what if I was in real trouble and need their assistance?