Getting a shop to pay for a shoddy work done

How do I go about getting a mechanic shop to pay for a shoddy work done on my equipment and the occurring bill for the repairs?

The story is..I went into a shop to get some work done on my trailer. Asked them to replace a bushing on one of the axle trailing arms. I dropped the trailer at their shop and came back the next day, picked up my trailer, inspected the work done the best that I could and paid the bill. Then went on with my work week. The next day after delivering my load 500 miles away and going to pick up another load as I'm driving down the highway I see one of my trailer wheels wobbling I pull over and see that both wheels on my front trailer axle have nearly fell off! They were held on by a single lugnut! Apparently once they put the wheels back on the trailer they didnt torque the lugnuts. Both steel wheels are destroyed and the wheel hub was all pitted by the wheels laying on top of it. So I spend the next two days getting repairs done by the only road service mechanic in the area that has the knowledge to do this type of repair. Most shops in the area said they are "not authorized" to this type of work. Had to replace both of the wheels, the wheel hub, the wheel bearings, the studs and the lugnuts. Which was a hefty bill.
I called the shop that had done the work on my trailer the previous day and told them what happened. The shop owner told me he will question his mechanic that worked on the trailer and ... The next day I called he said to me that one of his air compressors had a bad governor so it wasnt putting out enough air pressure. Told me he will pay the bill for the work I had to get done, to fax him the bill and he will send me a check. That was two weeks ago, now whenever I call they give me the run around or some ######## about the bill being too high and that I was overcharged for this and that and whatnot. As if I had a choice as to what I would pay for the work when stranded on the side of the road.

Long story short.. shop that did work on my trailer didn't torque the wheels properly which destroyed my trailer wheels, the wheel hub etc. Now they refuse to pay for the repair I had to get done due to their negligence.

 

The work was done at a shop in Dallas, which does all types of repairs on heavy trucks.

 

I have paid for all repairs with a credit card, but the work I went in for (replacing the bushing on the trailer) was done properly. Its the fact that in order to do that they had to take off the wheels to get access to it and once they finished work and put the wheels back on they didn't torque the lugnuts enough. The bill I want them to pay for is what I had to pay the other shop (road call) for the damages that happened afterwards.

I do have a lot of pictures of the damaged wheels and the hub, and everything being replaced. And I kept the damaged wheel hub and the studs.
I wanted to avoid taking legal action, it may end up costing me more in fees even if I do win the claim. Seems like that's my only option now.