Missed call on my cell phone, left no message.

I have been getting calls on my cell from a recorded woman's voice that says: "Before we run your credit, press 1"...etc "...or press 9 to be removed from our database." This number sometimes appeared with this "866" prefix, then it began to come in as "Unavailable." I never answered (I hope, luckily!) and discovered these calls as messages recorded on my cell phone voice mail system. I am being hounded! Calls come in constantly (which I can't answer while on the clock at work) to the extent that my voice mailbox gets full of them and cannot accept anymore messages, I think that this is harassment. These persistent SOBs are really pissing me off! Since I don't pick up the calls and they go directly to voicemail, I am worried that they are onto something with my number and that that's why they keep calling. I think that they are harassing and threatening and they need to be stopped.

this number 866-421-8400 calls our house everyday! Call ID says 800 service, whatever that is. THey Never leave a message very annoying and I have no idea who or why they call.