My (un)professional advice:
You don't need a lawyer - represent yourself and let the facts speak for themselves.
Send a certified letter to shop with the following information:
1.) A recap of the entire history
2.) Self explanation that you feel you've given them ample time and ample chances to fix it
3.) A list of what would satisfy you (or the one thing)
4.) A deadline set for a reply from them
5.) State if they are unable to meet your demands and/or fail to respond you will take them to small claims court
6.) You will ask for full refund, plus towing charges, wages missed from work from all parties involved and mental anguish.
7.) Reiterate you have everything documented, dates and times and prefer not to go down this road but will should they not agree to terms.
Much like lawyers - it's an intimidation game because the laws are already in the books.