Gather all the proof you have that you have paid child support to the child's mother. The courts generally prefer to have you paying child support and paying your arrearages rather than putting you in jail. If you can show what you've paid, you'll have some ammo to defend yourself. Also bring your tax returns and W-2s for the last two or three years. You should also consider filing a motion for enforcement of visitation against her and getting her served at the courthouse.