Small claims courts sort of march to their own drummer, and sometimes do not fully apply the Texas Rules of Civil Procedure.
But, I suggest that you write to the court to request that the court enter a default against the repair shop. You will have to have the return of service on file for at least ten days. You should collect the paperwork that documents your damages. If your claim is liquidated (a determined amount), you can request that the court enter default judgment for the amount of your liquidated claim (which should be no more than the amount for which you filed suit).
You would be best served by retaining an attorney for an hour's worth of time to help you prevail.
I fully agree with the prior answer. Also, make sure that the return of service is on file with the Court. That way the Court knows that the auto shop was actually served.
This answer is intended for informational and educational purposes only and should not be considered legal advice nor forming the attorney client relationship. This attorney is licensed in Texas.
I respectfully point out that even if you win, all you will get is a piece of paper called a "judgment." Enforcing a judgment and actually collecting some money on it is not a DIY project for a non-lawyer. Since you will very likely end up having to consult a lawyer in any event, why not do so now?