Received daily calls from this number on my Google Voice line (whose number I use with all of my credit cards).  If you try to call back from a blocked number, you will get an out of service recording. But if you call from an unblocked number (like from a burner/prepaid cell phone), you'll get a DiscoverCard greeting.  Sneaky.

When i enabled the "Block Caller" feature on Google Voice, that didn't stop them.  They called the next day from (415) 691-4660.  Same deal.  On a whim, I dialed 4660 through 4669 and they all answer from DiscoverCard.

Called twice, No message first time. Hung up second time