“Wait a minute. Can they block your number? I remember courts ruling that Trump could not block a constituent on Twitter.”
They probably don’t block per se, but they may “accidentally” hit the button to dump said call. They can then say it was a switchboard glitch, or the intern was overwhelmed.
Actually, were I on the other side of the call, I would not want to talk with me, either. It is their job, however, to deal honestly with their constituents.