Ever put your phone number on Craigslist, or ANYWHERE on the 'net?
I did (Craigslist) a couple years ago & I've been getting as many as 3 calls a day from various numbers. Some numbers are US, some foreign.
I used to answer them, but then either no one is there, or if a person was on the line, they would have a thick foreign accent, totally mispronounce my name (I tell them that there is no one here by that name!), or launch into some sales spiel.
I would tell them rather sternly not to call me again, FWIW!
I've gotten to where now I just reject the call, as blocking them causes them to just use a different number.
Looking through my contacts, there are 37 blocked numbers!
I've added my number to the "Do not call" registry, but it's been major fail so far.