It sounds like you have already done your research to make sure that you qualify for the Head of Household exemption under Florida Statute 222.11. The following is from a Florida Bar article:
"If the judgment debtor qualifies for and properly claims the "head of family exemption," then the judgment debtor is afforded two levels of protection from wage garnishment. First, the disposable earnings of the judgment debtor up to $750 per week are automatically exempt from garnishment. No exceptions. Second, all disposable earnings greater than $750 per week are exempt, unless the exemption is affirmatively waived by the judgment debtor in accordance with §222.11."
You can read the entire article here:
https://www.floridabar.org
Also, if you were not properly served and do not owe the debt, you may be able to have the judgment vacated. A consult with an attorney may be in order.