On CB I just saw in the direct messages if you click the vertical dots on a direct message you can "ignore user", not sure how this works exactly with CB and if it completely stops you being harassed by DMs or not, but if anyone tries it and lets us know, it'd be useful info
Edit:
Just looking in my Bonga inbox and testing, I see it too has a "ban model" option. So he can also do this on there. Click into the message from the model > click the 3 dots at the top > near the bottom "Ban Model".