I picked up phone, remained silent, didn't say "Hello." Obvious Robocall; computer terminated call after 15 seconds. Caller paid for the Toll Call. Some folks say "This merely authenticates your number is a valid number." Others, with whom I agree, say "If many irritated recipients of such calls caused the calling party to have to pay for the call, then their margin of profit would be diminished, and perhaps they'd take up other, legitimate, work."
Picked up silently knowing it was spam. DEAD AIR of a robocall. Other sites list this as a "REVERSE MORTGAGE" SCAM; PHISHING for SS# and FINANCIAL Info. This is a CELL PHONE number; another sign of a SCAM. Love how they target SENIORS. Not all seniors are stupid, senile or uneducated.
Robocall - left no message. sent them a text saying "This number is listed as DO NOT CALL. You are in violation and will be reported.
For others... you can set up an automatic reply text message saying this so when you get a call from an unidentified #, just hit 'send message'. If it's a cell number they will get the message