Robocalls Causing Phone to Ring

The Verizon FIOS telephone DND service worked fine (forwarding all calls to voicemail) for many months up til now.  Recently robocalls have caused our phone to actually RING, which is what we don't want to have happen.  I spent an hour and a half on hold for Tech Support yesterday, then some time talking with the rep.  He said he'd re-set our ONT.  But today, again, a robocall caused our phone to ring.  I am now on hold for Tech Suppot for an hour and 39 minutes, and still waiting.  I'd really like to keep this "landline" but maybe I should eliminate it, as others I know have done.  Already I have to tell friends to call my cell phone if they want to get through to me faster.