if this happened on the way home from the shop you should have called them to send a flat bed and fix it the right way so you wouldn't have to call your lawyer. I hate shops!
in a tune up on my magnum V8 its easy to break the oil pressure sending unit but that will let all your oil come flying out (will empty the engine in seconds). if the check engine light is on have it scanned, sounds like a crank/cam sensor. How does the exhaust look? is it blue? white? black? is it knocking? clicking? rattling?
when you run it now do you get oil pressure? if so when does it drop? during acceleration? Stopping? hard turns? any of those would indicate low oil level.
I suggest reading your codes, since its a DC product you can hit the key 3 times and it will flash the codes in the check engine light.
this will help with reading the codes.