Los Angeles Parking Violations Bureau Refuses to recognize official DMV's official Release of Liabiltiy Internet

My friend and I shared a car. We gave it away on 6/22/12. I forgot to send in the stub releasing liability and the new owner started getting tickets. I mailed a substitute Release of Liability form, per the DMV's instructions, and then wrote to the DMV in Sacramento asking for, and subsequently received, proof that we had released liability on the vehicle on June 22 of 2012. At that point I had proof of Release of Liability on 6/22/12 in hand. We sent a copy of that proof to the Parking Violations Bureau, per the instructions on the notice we received about two tickets in Los Angeles. But the PVB of L.A. responded by mail saying we have to pay the fines in order to get a hearing to present our case. But we have already presented proof that released liability of this car. By it's very definition, this means that anything that happened after 6/22/12 has nothing to do with us. Why should we have to do anything - especially lay out money before they will stop threatening us? If we released liability, which we have proven with a document from the DMV, then that means we are not liable. Can we sue? Can we do a class action suit? Does any attorney want to help stop this outrageous and illegal policy of the Parking Violations Bureau?