GRAHAM G.

Washington DC is renowned for giving out nebulous parking tickets with no reasonable way of disputing them. They feed on tourists.
A parking dispute will take 6-8 months for a decision.
If the infringement is paid, the dispute is terminated. (No further action is permitted by the government.)
If you don't pay and you lose your appeal, the parking fine is doubled.
If you are in a rental car, the rental company will pay the infringement anyway and charge you a 15% (typical) administration fee.
The ombudsman (an official appointed to investigate individuals' complaints against maladministration, especially that of public authorities) just reiterates what the government does.
I recommend protesting with your feet - don't be a tourist in Washington DC. If you do go, visit the National Mall, Lincoln Memorial, Washington monument and Capital (can all be done in a day) and get out of there.