Robocallers who mumble

The robocallers have sharpened up their game this month.  Used to be, I would pick up the phone, and then wait five seconds.  (one thousand, two thousand ...) If the robocaller failed to answer within 5 seconds (fairly common) I would hang up.  Now, the robocaller picks up the phone after 2 or 3 seconds and starts its spiel.  If the robocaller mumbles, so that I cannot understand what company it is calling from, I hang up.  If the robocallers suggests I press 1 (or any number) I hang up.  

We need a law criminalizing robocallers.