A group of Dallas surgeons fired one of their billing experts because she refused to aid them in a "massive and pervasive health-care fraud scheme," according to a lawsuit filed this morning. Cortez Mills is suing Texas Vascular Associates and its nine doctors, saying they pressured her to commit "criminally illegal acts" against patients, insurance companies and Medicare, the federal insurance program for seniors. Among the alleged practices: double billing, "upcoding", "balance billing", and "drive-by billing" (charging patients when a doctor merely watches another doctor work).