If the child support has been paid, it is unlikely that you would go to jail. Make sure that you have all documentation of the payments that have been made, since different government departments do not always communicate effectively with each other.
As to the issue of modifying the current child support, you will need to file a Supplemental Petition to get that modified. It is possible that the court would address it at the contempt hearing, but unlikely.
You will not be able to modify child support obligation without filing a supplemental petition to modify child support, and allege a statutory basis for modification per 61.30, Florida Statutes.
Consult with a family law attorney to better understand your rights and responsibilities.
You must go to court unless you receive paperwork that the hearing has been cancelled. Bring all your paperwork and make sure to bring anything you have showing that the balance is zero.
Regarding your modification, you must file a Supplemental Petition for Modification and you must serve the other party and give the other party an opportunity to respond or answer the petition before you can go to court to change your child support amount.