My question involves collection proceedings in the State of: Texas

I live in Ohio. In October 2005, my daughter had surgery in Texas with a non-participating surgeon of our health plan. We paid the surgeon $5000 upfront because of this reason. Our insurance left an unpaid balance of approximately $26,000(over UCR allowance). We received a balance due bill from the surgeon in May 2008. I sent a letter in June and subsequently hired an attorney to call the surgeon's office in July to negotiate a settlement. They have not responded to him or me. Since the Texas SOL is four years, my question is, assuming no more contact from the surgeon's office, from what date will this debt be beyond collection--four years from the October 2005 surgery, the balance due bill date of May 2008, or the last contact made with the surgeon(attorney call in July 2008)? In my letter, I did acknowledge the debt as valid. I stated I could not afford the total balance.