Got a missed call from this number, attempts to call back are met with a generic voice mail message.

Marketing scam call for website sales, they found my number on a Gumtree Ad, and wanted to confirm my email address so they can supposedly post my ad. Well that is just dumb as my ad has been posted over 1 year ago, so all they really want to do is perform hacking of private information. Just hang up or block the number!
Note that the caller had no affiliation with Gumtree.