Don't determine later if a lawyer is needed. I'll help you with that: you need a lawyer. Had you gotten a lawyer, you'd have known to file a petition to modify support months ago. You need to file a petition to modify support to cease ongoing support and to set a payment plan on the arrears. The arrearage can't be modified without the other parent's permission.
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Unless you agreed in the divorce to pay support post-majority support (e.g., college expenses), your obligation should terminate upon your child's graduation from high school in June. But as Mr. Rose warned you, a modification in Florida only will be granted to the date you file your Petition; therefore your ongoing child support cannot be reduced based on your reduction in income. Nor can your arrearage be reduced. However, as child support should be terminated in June, you should be successful in establishing a reduced amount of payment towards the arreage based on your current income. You should file a Motion to Terminate Support, Establish Arreages, and a Reduced Payment on Arrearages as soon as possible. You can get the paperwork necessary off of your clerk of court's website or you can go to the clerk's office to pick up a package of the necessary paperwork. You probably want ot at least have a consultation with an attorney as your case is not complex (for a family law attorney) in terms of the necessary filings and dealing with the Department of Revenue so the attorney's fees should be quite reasonable. But time does appear to be of the essence in your case. If the Department has an Income Deuction Order they will continue to take the full ongoing child support amount each month out of your paycheck to apply towards the arrearage until you obtain relief.
Family law rules differ significantly in every state, especially procedural rules. Always seek the advice of an attorney in the state where your divorce was filed.
The information you need is the name and address of a lawyer, but you can determine if you need one or not. Just file all the right documents and it is all taken care of. Just write a long, long letter to the judge and be sure to send a copy to the ex, or her attorney. It does not work that way. What you need to file is called a supplemental petition for modification. You cannot reduce the arrearage, as past due child support is the vested right of the child in Florida, without an agreement with the other party. Why should she agree to reduce it?