Identify point of contact at insurer regarding subrogation process

I am an injury lawyer. my client got hurt a car crash in July 2015 and got medical care. care was paid by her medicare advantage plan, in Texas, until a date in 2016 when my client converted to traditional medicare. Federal law gives MedicareAdvantage plans the right to demand their money back if the member gets money from a careless driver's insurance. I need to identify the point of contact within the specific medicare advantage plan provider-administrator for the dates 2015-2016. The Plan was called TexanPlus. I need a name, email, website, physical address, fax. This private company operates under a contract with the federal government and the federal government shares with this company the government's powerful rights to get paid. I have to be able to prove I made the right efforts to get their attention about this matter. It is likely that the "how-to" data was contained in some paperwork my client got in 2015 or before whenever she first signed up for TexanPlus, but she does not have that paperwork to look at now.