Harris County prosecutors complained to federal Medicare authorities for at least two years that rampant fraud involving private ambulances across the region was costing taxpayers millions of dollars, but say their concerns were ignored. "We have been beating our heads against a wall for two years now," Harris County District Attorney Pat Lykos said Monday, a day after the Houston Chronicle reported that Harris County leads the nation in the number of private ambulance companies, vehicles and Medicare payments. "They're totally unresponsive. This is tens of millions of dollars being wasted. This isn't rocket science." Lykos' office provided the Chronicle Monday with letters and records documenting prosecutors' frustration since 2009. "We need Centers for Medicare and Medicaid Services to address this staggering and out-of-control problem," Lykos wrote last year to Centers for Medicare and Medicaid Services Acting Director Jonathan Blum, calling Houston "the epicenter for a massive Medicare fraud scheme."