My suggestion is for you to contact a local attorney and have the write a letter to see if you can get it resolved through that method. You want to use an attorney because, obviously, they are not responding to you.
As far as filing suit, if the amount you are seeking is under $10,000 in Texas you can file in Small Claims court (Justice of the Peace court). The process follows the following procedure:
The process of a lawsuit is essentially the same everywhere, with a few, minor procedural differences.
A lawsuit generally follows this process:
1) File the petition in the court with jurisdiction and venue. The court with jurisdiction and venue is usually where the defendant resides or has their place of business. You also have to look at the amount you intend to sue for to determine what court is correct
2) When you file the petition with the clerk of courts you will pay the filing fee and also ask for citation to be issued and service to be done. The clerk doesn't serve the papers so ask them if you have to take them to the sheriff's office for service or if they will do it. Just follow their directions as to that.
3) The sheriff will serve the defendant with the lawsuit.
4) The defendant will file their answer.
5) You can then do some discovery if necessary but you will need to check with the clerk and ask if your court allows discovery. Some small claims courts do not.
6) After that the next step is to set the case for trial.
7) During the trial you introduce your evidence and they introduce theirs.
8) The judge renders an oral judgment and a written order is made based on that oral judgment which the judge then signs.
That is the basic process of a lawsuit.
If your question has been answered then I'd offer my best wishes to you and ask that you please not forget to leave a 5 Star Positive Rating so I receive credit for my work. Of course, please feel free to ask any follow-up questions in this thread. I want to be sure all of your questions are answered.