I recently got a new car and I have had some problems with insurance?

I was at the dealership on September 1st, 2010. I received an offer for my vehicle and with that money plus some extra I was going to buy a new vehicle. I don't make stupid purchases I can't afford so I called my insurance company and gave them boatloads of information so I could try to understand how much my premium would go up per year. I had previously a 1998 Honda Accord and I was going to switch to either a 1997 Lexus ES300 or 1998 BMW 740IL. Upon giving my insurance the information they plugged the information in and told me that my insurance on the BMW would go up $900 annually. I reasonably declined and asked them to look into the Lexus. They then told me that the insurance would go up by $89 annually. So I agreed to this, $89 not being too much and I sold my vehicle and proceeded to buy the new Lexus. After getting the car I went to the insurance office, got my forms stamped and went to the RMV to register the vehicle. I registered the vehicle and about a month later I get a call from the insurance company telling me that there is a problem with my insurance. So I go down there and they tell me we made a mistake and that they're sorry, because instead of my Lexus being insured, they still had insurance on my old Accord. They handle this problem and then they tell me that my premium is going to go up by $435 a year compared to the $89 that we agreed on earlier. I am not okay with this jump. The phone call between me and the insurance company on September 1st is recorded, and I'm waiting on their call back, but what the hell can I do to make sure they stick to their commitment of $89.