Are you crazy? First of all, simply don't answer the call if you don't know who's calling. Second, don't ever call them back. Either way, you are confirming you have a viable number and you will find yourself on many new lists. If they're legit, they will leave you a message.
Called and asked for my daughter on my phone (under another cell phone company plan a few years back, the account/number was under her name), When I asked who they were, they hung up. I tried to call back and got a busy signal. >:\ Going to block.
Rang 1 time then stopped. No voice mail. Blocked the number. Don't call a number back if they don't leave a voice mail. You're just asking for trouble. How important can it be if they don't leave a voice mail. Numbers I dont recognize and leave no voice mail are blocked from any future calls period. You need to acquire this mentality to stop this insanity. It's not hard once you do it a few times.