No voicemail on my line, but calls are being sent to VM for a different number

[micren]

We signed up for a landline through Verizon in December. We did not sign up for voicemail, but we just realized that callers to our number are being forwarded to what appears to be someone else's e-mail box after just a few rings.

Callers get an automated message after about four rings that says they have reached xxx-xxxx (the other number that isn't ours). The other number has the same exchange as ours, but the last four digits are different.

I have verified that our account does not have voicemail (by checking our account details on the Verizon website).

I have verified that our number is not call forwarded to another number (by dialing *73).

I've tried logging on to voicemail using the access number and password provided by Verizon, but it doesn't work. When I call the voicemail access number, it tells me I am calling from the other number (not ours). When I indicate on the VM access line that I am not calling from our home number, and punch in our home number, it STILL says I am calling from this other number. 

I cannot figure out what is going on. Any ideas?

Thanks.

[micren]

Just realized in the first paragraph, that should say "callers to our number are being forwarded to what appears to be someone else's VOICEMAIL box after just a few rings" (rather than e-mail box).