It will be worth your while to talk to a lawyer about this. You could, depending on your particular situation, of course, ignore those notices. It depends, though. Call a criminal defense lawyer who is familiar with the issue, it'll be worth it. I bet you'll find one to talk to you for not very much.
You should be careful and consult an attorney in your town in Texas. A theft conviction can have long term effects on getting a job, or housing. If a non citizen there are also possible immigration consequences like deportation. Theft is a crime of dishonesty or moral turpidute and can be used to impeach you if you are a party in a civil case or a witness or a defendant if you testify at trial or hearing.
Regarding the attorney letter I have advised clients in Colorado to ignore it. It is unlikely he will sue you to collect this small amount. However check with a local lawyer.
All the best