You (anyone as well) have enough to work with.
Did he actually show you a cease and desist request and not let you keep it? Or do you have a copy of it you can share.
If he does not have a copy of it in hand they did not serve him. He also has to sign for it officially. There is a process. If that did not happen a court cannot honor it.
He looked at it, and there were witnesses, it's enough. Ad we have recorded the majority of the conversation as well. Should be enough to sue for damages of business and a few other fun things. But we're considering going a different route in the mean time.