You should never press any numbers, just hang up. When you respond to the call (voice, numbers, etc) you're confirming to their computer that it has reached an active, valid telephone number!
See the FTC video on robo-calls. Very informative.
I just got my first call from this number - let my computer answer it, play the SIT tune, tell them to never call again, and disconnect. Their computer will only "hear" the SIT tune and (hopefullly consider it a dead number). I use PhoneTray software - you can still find free versions online!