Finally getting to it!!! 1970 Duster 340
Stories like this happen more often than people like to share. The work needed was obvious when it was dropped off. It's not like there were any surprises. An agreed upon price and a request for a call if anything changed may have prevented this, maybe not.
The shop owner, who is directly responsible, is either incompetent or dishonest (or both). He may even have hopes of you abandoning the project and he ends up owning it. He probably has a barracuda for a lawyer. Guess he doesn't care about his reputation.
Just went through a small situation with a powder coating company doing a Saab Viggen valve cover for a car I'm selling. The buyer lost interest and bought another car. I gave it to the shop with "blind faith".
Sorry to hear about your situation. Wish I kept my '70 Duster340 I sold 43 years ago. I'm sure yours will be beautiful when it's done. Good Luck!