this number has been doing hang up calls to a cell phone i own

Caller did not leave message.

Returned call, male recorded voice said it was the number for US Prescription Benefit card. Gives details about who is eligable, asks for name & address to be left on answering machine due to high volume of calls.

This number called my cellphone and hung up.  What's with that?

I have NEVER gotten spam calls on my cell phone before this.  Who is it?

Called my cell phone at 7:37 am