unknown caller, but won't leave a messag

Getting people to agree to be called by a diabetic supply company.

they call constantly, no one is on the line when you pick up, silence and a click.  no voice messages left

when I pick up the phone, no one is there and then click.  When I called the number back, nice music with intermitten "your call is important to us, please stay on the line and someone will be with you shortly".  After a while, "Good-bye" and that's the end of the call.

it's a con