Who is this and why are they calling me

Left no message. I don't know number so I no answer.

Agreed called x3 no message left

call and won't say anything

They have called twice in the last week. I will not answer numbers I don't know. They do not leave a vm. Very annoying because I have been in and out of hospital and have trouble sleeping, this number always seems to call right when I do fall asleep. Turning off my phone is not an option.....