Network Operator Services Zero Plus Dialing - ZPDI phone company ripoff - unwilling to respond Longview, Texas

This long distance company charged me for a collect call that I did NOT receive.

I know that someone did try to call me collect when I was not at home.  I found part of the call on my voice mail when I returned. 
When I got my phone bill, there was a charge of $29.94 for a 5 minute call that they say went through.

However, I wasn't here that day, and no one else has access to my home or phone.
When I called the number for Zero Plus Dialing, they transferred me to Network Operator Services.  NOS insisted that I must have authorized this collect call - saying their system is never wrong. 
NOS offered to take off $11 of the bill.  When I insisted on talking with a supervisor to get a full refund, the supervisor offered to take off half of the bill ($15).  When I asked to talk to another higher-up supervisor, they refused to do so and said there was no one that they could give me the name of.  When I asked for a phone number to reach a supervisor, they insisted that they did not have a phone number for the supervisor or corporate office.  They said the only way I could reach someone would be to write to a post office box.

Really?? A long distance phone company says they don't have a phone number for the main office?
This company is a scam.  A legitimate company always has a way to talk with someone in charge. And a legitimate company always has a way to correct their mistakes.  A legitimate company doesn't spend 30 minutes giving someone the run-around and refuse to give them a way to talk to an appropriate person.

Really??  $29.94 for 5 minutes - for a call that I did not receive.