Keep or make a log of all the calls he has made, yes the ones you haven't answered and include this one with the gist of the conversation.
Also note his obsessive behavior at meetings etc. Take that log to the police and report him as a STALKER. Once the report is written, that gives you the ammunition you need to go to court and get a Restraining Order to keep him from contacting you.
If he violates the order you call the police and he goes to jail. He will get the hint.
J M H O
Love and hugs,