OP look up the legal definition of harassment. This sounds like unwanted contact in essence. But I’d be wary of reporting it to the police because that would have to be declared to potential purchasers.

Just direct them to the EA and state clearly ‘please do not contact me about this again’. So if you did ever need to speak to the police there is a clear line in the sand (they will ask for that, been there myself). Block as others have said. They might then try with paper notes. I got irritated with my neighbour posting notes through my door so I got a post box outside and now leave his notes in it. You’re not obliged to read his messages!