Several thoughts --
1. Since the Florida Retirement System is a state pension, it is not subject to any national regulation. If anyone mentions the word ERISA to you, ignore them. Any rights you have are a creature of Florida Law.
2. What kind of notice did you receive initially about applying for DROP? If you weren't told when you became DROP eligible, there may be something worth investigating there. Also, was your initial contact date (March 2020) inside or outside your DROP window? There is a concept called promissory estoppel that may apply, but probably only if you missed the deadline because of bad information. If your deadline was already gone, though, you have a harder road to a benefit..
3. Have you tried contacting the office of your state representative? (Either state house or state senate). They may be able to help you with the state agencies.
4. You may want a lawyer to advise you. Be careful, though. Also, you may want to get in touch with the Pension Rights Center.