I just had an experience similar to the ones already posted: a female called my mother's home phone saying she needed to verify my identity. Within an hour, a male called and said I was being subpoenaed and he needed to speak with me ASAP. I called and was floored by the unprofessionalism and threatening tone, included that it was urgent because a subpoena was going to be served at my workplace today, and he had the last 4 digits of my SSN. He also offered to transfer my "debt" to one of my credit cards. When I expressed confusion and disgust, including that I don't have any credit cards, he argued that they've investigated me and they know I do, and started rattling off numbers. We then got disconnected. He tried calling back twice and left one voicemail. This must be stopped!!
Hate to break it to you but a lawfirm is a collection agency in the manner that they just have a lawyer on staff to write a lawsuit. If they are a third party in which they bought your debt they can get away with it. it is only when the OC acts as a collection agency is where things can go wrong.
Under the Fair Debt Collection Act they cannot threaten to sue, send a subpoena ect unless the actually did it. They are subject to the law. If I were you I'd sue them myself rather that get Texas to do anything.