If you want to file a complaint with the State Bar of Texas, go to their website and look under "public". They have the forms and all the information you need on-line.
Please don't misunderstand me, because I'm not being unsympathetic. It's more that I'm confused by your question and I'm not sure about your goals.
I'm not sure that you're only intending to ask about filing a complaint with the State Bar.
I'm not discouraging you from doing that, but I'm not sure what your goal is. If your goal is to see that their conduct is investigated and that any misconduct is punished, then that may be the route to take. But that's not a very effective route to change your own situation.
Of course you're angry and frustrated. But has the delay ended up jeopardizing the performance of the agreement reached at the mediation, or has your new attorney been successful? He or she is probably better acquainted with the background than any of us reading your question here can be. Is there some reason you haven't asked him or her about this?