OP, I don't think they will follow what community members suggest. Would you please create a flag, as TwitchySeal already suggested? If they want to prove that they are not guilty and maintain their reputation, They will have to go with 3rd party mediators. You have already Invited them, and other members also asked if they will cooperate with 3rd party mediators. Create a flag and add the link to the OP.

BTW, Coinplay already has an inactive flag created by bachezy for a similar case which can be found from here https://bitcointalk.org/index.php?action=trust;u=3502111;page=iflags. Until they solve the issues, Avoid Coinplay.