My center manager also accused me of insurance fraud. Told me that I wouldn't be allowed to return to work (after vacation -- had gotten injured, thankfully nothing major, a week prior and was working with restrictions) until I had a meeting with Liberty Mutual, the company attorney, the DM, etc, and my union steward. I laughed and told him I'd advise my lawyer, but that I could already assure him that no such meeting would take place without my lawyer. "The union will be there to represent you." "Yes of course, and my lawyer too." That meeting never happened lol.
If you got work injuries treated via your insurance, rather than work comp, that's no good. If the insurer finds out, they can and will bill you. Don't let the company intimidate you -- if they ever try again, file Art 37 on them and hold your ground. Work injuries are the company's responsibility. Also, here anyway, short term is a larger pay cut than work comp, and FMLA doesn't pay a dime.