Oh, the joys of Facebook! For clarification, is the previous chair still a councillor? Is the good news element of the failed appeal your personal opinion, or the view of the majority? What was the PC's opinion on this? Were you asked by the PC to attend as their representative? If not, you attended as a member of the public. What information had the PC gathered and how?
The answer to your main question is that you cannot do anything via the PC. If the former chair is still a councillor, you can submit a code of conduct complaint to the district council's monitoring officer, whose powers are limited, so it is unlikely that they will go beyond a cursory investigation of the facts. You are, of course, free to pursue this privately, but it is unlikely that the Police will wish to get involved unless the wording of the communications breached any of the statutory triggers. What would happen if you do absolutely nothing? Just a thought.