You are out of sight and out of mind. Show up to the shop with the truck. Show up in the morning and spend the day. Things always go different face to face. You will either get results or know you need to move on to the next step. When I have issues, I try to show my face. It's easier to communicate that way.
I would really be cool with him/them and try to get them to perform up to their good name... if they have one.
On calling lawyers, and lawsuits. My guess is you've never been down that road or we would be reading the word Attorney after a legal victory. My advise is leave the attorney word out of any and all of your correspondence written and verbal. Nobody likes to be threatened with a suit, that is just about the ugliest thing a business owner can hear. Businesses get ruined by lawsuits, attorney and lawsuit are not words to use lightly.
Being face to face with the business will help to ground you and you will do better, I am certain.
Hold more tightly to your hard earned bucks and make certain of what you're paying for! A quote from Albert Einstein. "The only source of knowledge is experience."
Good luck!
j