Keep getting calls from this number - I pick up, but because the number is not familiar to me, I don’t say hello, and it disconnects. Tried calling it back and it says ‘this number is not connected’

Just had a call from this number offering Home Improvement services. Not interested and number now blocked.

I didn’t answer, but when I rang back it said your call could not be connected

This number always calls and disconnects. Why????