claiming expenses for reimbursement from two different sources would generally be considered fraud. It is a civil matter between you and the people you defrauded until the police get involved. Then it is both civil and criminal (though they may not care unless the $ amount is high enough and the people you defrauded want to press charges). Depending on who you defrauded (govt agency, bank, etc) they may have already brought in law enforcement.
Suggestion: pay the money back ASAP before they decide to have you arrested. Perhaps a call to a lawyer would be in order