There is a consumer protection office at the government office complex at Chaeng Wattanna, Bangkok.
My wife used them when we had a problem with our truck and the main dealer was unhelpful.
They set up a meeting between the two parties and listened to both sides of the story.
After no agreement was made, they suggested my wife take the dealer to court. They did all the paperwork for her. Finally, on the day of the court hearing, a settlement was made, (Which we were very happy with) 'Out of Court'.
This was a free service. We paid nothing.
Don't waste your time with the police.