A federal audit of Maryland's health insurance exchange found that the state improperly billed the government $28.4 million and should return the money.

According to the inspector general of the Department of Health and Human Services, though there was no fraud or criminal wrongdoing, Maryland misallocated costs to federal grants instead of the Medicaid program in 2013 and 2014, and failed to use updated enrollment data once it was made available, the Associated Press reported.

"The state agency misallocated these costs because it did not have adequate internal controls to ensure the proper allocation costs," the audit said.

Maryland received an extra $15.9 million due to a 37-percentage point difference in the estimated enrollment and the actual enrollment numbers provided to the federal government. An additional $12.5 million was misallocated due to flawed Medicaid enrollment estimates, reported The Hill.

According to state officials, the contractor responsible for the miscalculations was the Hilltop Institute at the University of Maryland, Baltimore County, reported the Baltimore Sun.

Maryland health officials disputed the findings and said they would not refund the money, arguing that the inconsistencies were the result of vague federal guidelines, which they say didn't require updated enrollment figures. The auditors insist their findings and recommendations are valid, and urged the state to refund the misallocations, according to The Hill.

Former Democratic Gov. Martin O'Malley, who oversaw the launch of the health care exchange and is considering running for president, highlighted his technological and data-driven approach to government efficiency and accountability and had hoped to set an example with his state's health exchange rollout. However, it ended up being one of the most flawed in the country, noted AP. The state's health exchange website crashed on its first day and was plagued with glitches.