I have a cell phone with number beginning with 650-521-xxxx. Practically every day, I get a robocall from a number beginning with 650 area code and 521 prefix, but changing last four digits. I ignore and add them to auto-reject list, but they keep coming and cannot be stopped because they keep changing. In the instances I answered by mistake, I have heard the same message, which started with: "You have been selected by Expedia" or something like that, possibly related to a cruise.

Here are the numbers I have seen in caller ID so far:
650-521-9048
650-521-7854
650-521-9982
650-521-5383
650-521-3294
650-521-8385
650-521-9124
650-521-8271
650-521-7811
650-521-8715
650-521-4884
650-521-4493
650-521-3199
650-521-8276