Not al numbers that come up on Caller display as "withheld" are necessarily scams, which makes life even more difficult. Both my son's and daughter's numbers show as withheld, for reasons to do with their respective jobs, as do any calls from the doctor's surgery or hospital (as mentioned above) so you can't really NOT pick up the phone, in case it is a genuine call.
As for Amazon, the latest trick seems to be phoning to tell you that there's something wrong with your Amazon Prime account, and you need to re-confirm your payment details. If you actually have a Prime account (I don't!) you could be taken in by this, as was a rather gullible friend.