What are my options (or any advice you can offer) when a mechanic has negligently repaired something?

Basically, our cars motor was running fine, but the transmission was shot. We took it in to get rebuilt, and have had some shady stuff going on with the mechanic.

After lying to us (and admitting to it afterwards) about a broken part, we found that the car will now barely stay running. It is much worse than when we brought it in, and the part that they broke which they are now repairing (which they are saying is causing the problem) should not be causing the car to do what its doing, based on my previous experience with that part on another car.

He is repairing that part, but I would like to know what my options are if its still running badly afterwards and he tries screwing me over. I've contacted the tire place that did a simple inspection on it a few months back and they are going to try to put something together as proof of the cars prior condition, but i'm not sure if that'll be enough. What are my options? Does anyone have any suggestions or advice?

Added (1). Now he is saying that they found something else wrong with some kind of converter and thats what is causing the issue. He is vehemently denying that his shop did it, although my car was running smoothly before he touched it. He is now offering to replace that part, but I htink he expects us to pay for it. I've got my state inspection record and inspection from firestone as well all done within the last 3 months. Maybe that will help… I'm feeling completely powerless right now.

Added (2). Oh and the part that they originally broke, which they said was causing the issue before this new thing, was the throttle body hose. BTW they also broke the snaps that held our air filter box and used sheetrock screws to screw it into the plastic.

Added (3). 2006 HONDA ACCORD, AUTOMATIC, TEXAS

Once you get the car back, run away from that guy and go to someone more reputable.

I would call the county attorney, or the better business bureau they can tell you your options and put the pressure on the mechanic to make it right or pay to have it made right. Don't let up on that guy.

My advice to you is that if you are actually wanting a viable answer to your questions, that you give the following info because without it, a meaningful answer is just freakin impossible:

Year, make, model, engine and trans type, and the state you live in!

Without any real detail all anyone can say is fins another mechanic and GRT a refund from this one or sue him.

"it is much worst than when we bought it"? What part are you talking about that is broken?