Calling my cell phone leaves no msg

Calls several times a day but won't leave a message.

Hospital marketing research

Calls incessantly and does not leave a message.  Caller ID lists them as "unknown". After the 30th call, I called them back from the caller id.  Got a snooty female "service rep".  Asked her who they were and why they call and do not leave a message.  "Hospital survey"  Why do you not say that and why do you "spoof" the number?  Snooty reply " that is not our protocol".  Wanted my name and number to call me back.  What idiots.  If it is important and valid, why do you not leave message and spoof the number?  Arrogant.

Calls my cell while im at work and wont leave a voicemail.