Hang-up calls, probably "Cardholder Services," who call me all the time in spite of repeated requests to remove my number., or some other scammer or phisher.  Reverse look-up shows Telcove of Vermont in s. Burlington.  Phoning 242-4334 yeilds, "You have reached the campaign voicemail.  Please leave a message."  Of course, campaign calls are exempted from the do not call registry, so this obviously is a scam.

Have been getting lots of calls from this number.  No answer when I pick up.

I got the campaign voicemail also when I called the number.

So when they called back, I did my best Japanese impression.   I don't know Japanese!   I think that worked, I suspect they won't be calling back.