I find such calls seem to come in slow waves.
Someone once told me, but I cannot verify this, that if you ignore, block or refuse several in a fairly short time they put the word around not to ring your number. Eventually the list disappears or different gangs spring up, and off we go again.
My land-line telephone does not display the calling number, so I cannot simply ignore it. I can interrogate it afterwards but that won't help because I cannot block numbers that anyway, are quite likely changed frequently. My 'phone does hold notifications of both messages and callers "who left no message". Most of the latter are probably fraudulent and I just ignore them.
Recorded voice messages are easy to identify as such. Live callers are easy to dismiss - sometimes I call them "liars" then hang up before they can.
My portable telephone is mercifully free of such antics, perhaps because it is too basic and too little used for the gangs to spot.
....
The most dangerous are not 'phone calls but e-posts pretending to be from genuine companies like banks; stealing their letter-heads and even the security advice and phishing-reporting links!
The latest was from HBSC, it said.... I soon spotted they had carefully reversed two of the initials, the "View Source" tool revealed routing via at least two, strange sender and domain names... and the dead give-away, I have never had an account with the real HBSC bank. I forwarded it to the phishing-report departments of both that and my own banks.
