Back Child Support Included Until Paid Off

My ex and I agreed, in writing, journalized with Ohio court, that my monthly child support obligation would be increased by a certain amount until the arrearage the court said I owed was paid off. I continue to receive letters from the County child support enforcement bureau saying I am in arrears. My most recent letter said my passport could be revoked. I plan to vacation out of the country soon. I've spoken with my child support bureau and they tell me this is standard procedure and that they don't recognize these types of agreements, although they are reducing the amount of the arrearage with each letter I receive. This leads me to believe that they are recognizing the agreement. My current arrearage is $3,000. How concerned should I be that my passport will be revoked, that any federal income tax will be withheld or that in the regular course of living, I am labeled a criminal? While I acknowledge that back support is owed, my ex and I agreed to repaying it as outlined above. Also, can I now make a lump sum payment and just be done with it?