The one earnest question that will ALWAYS make scammers hang up immediately:
"In case we get cut off, what phone number can I call you back on?"
If they actually give you a number instead of hanging up (which has NEVER happened in the many times I've used this line), just hang up immediately and call them back, to see if they answer.
1. Ignore voice messages
2. Ask pointed questions to any live caller, esp. one calling from a new number and asking for money...