Had the exact same thing happen to me about 2 hours ago--I didn't answer, called back, got the "this number is not assigned" automated message. Definitely spam. Do not bother calling back, and definitely DO NOT press any buttons they may ask you to, should you call back.
received a phone call from this number twice. called it back, it rings once and goes directly to sayig it's not in service. don't pick upa phone call from this y'all ;) just a waste of time