Patient and Physician Billing Services - American. (9 days ago) Date of Service 10/1/2020 and forward: 1.888.987.7983, Patient Service Portal. Texoma Medical Center Date of Service prior to 10/1/2020: 800.378.4134 Date of Service 10/1/2020 and forward: 1.888.987.7983, Patient Service Portal. All other Texas: 1.888.987.7983, Patient Service Portal..