Keeps calling... Silent and hangs up when I pick up... Various searches yields invalid phone number?!?!!?!?

Even after blocking this number, somehow I am still getting notified of missed calls from this number, on a daily basis.

Got a call this morning. Did not answer. Caller did not leave a voicemail.

Some guy conducting a survey. Asking about retirement options and if I have a mortgage.

Can't block this number as it comes up as invalid number.
Look up Google for "invalid number" as this will give you more
technical information.
Suggest you give this number on your phone a name of "invalid"
and then just ignore it when it rings, I know it's a pain when it rings,
but one day we might have a solution. Cheers

Caller disconnected when I answered

a couple calls of late, but no messages left

Another number to block