Same here. Two calls yesterday, ID on both was "unavailable". No message. Just got back from a 7-day road trip and had 15 calls on my answering machine... not one was a valid call. Out of the 15 calls, 7 were "blank" messages, 6 were no message at all, and 2 were that Apple scam message. Just venting, but I am sick & tired of not being able to answer my phone when it rings, and old enough to remember when that wasn't an issue!
I got a call identifying itself as some (medical) brace company and asking "Can you hear me, OK?". I had heard of the scam where scammer will paste your "yes" signature as your consent to some ridiculous offer. I answered "forget it, who are you?" and hung up. I don't know if the promoter still sold me some product/service, I do't care for at prices, I won't even consider. Who knows?
The 'yes' scam is merely a rumor and can be ignored. What you should do is just block the number and ignore them. They can't charge you simply by calling and asking if you can hear them. If they want to pull a scam, they could say yes themselves. As long as you did not give any personal info or confirm any, you should have to worry over a call.