short ring (no voice message left) 10pm on a weeknight

[Have previously had at least 3 hang-ups from this mumber all late at night]
Got a call at 10:45pm on a Wednesday night - caller had extremely heavy Russian or Slavic accent that was impossible to understand, said something (sounded like it was in English but totally incomprehensible) - then hung up.
CALL DURATION: 11 seconds.
ANNOYANCE FACTOR: 150,000,000 out of 10 as I had just managed to get to sleep after a day from hell

Unsolicited call - claimed to be from National Business Academy’ or something like that. Extremely rude - called back 3 times before I could block the number - beware!

Someone in the UK trying to get me into Bitcoin