Need the land line to this company

I received 7 calls today that when the phone is picked up, all you hear is a dial tone.
When I tried to call them back, I received a recording that says, "We are sorry your call cannot be completed as dialed." It has been going on for weeks where I receive numerous calls during the week (primarily working hours).

Did you find out who or what.....I keep getting the same thing

This number calls our car dealership all of the time, all hours of the day and night, and has been doing so for the enitre time i have worked here. It will either be silence on the phone or just a beeping noise. What is calling constantly? It gets very annoying. There are 2 numbers that call constantly, 214-572-8820 and 214-540-5503.
Who are they?

Faxing my cell phone.  Followed by another call from 214.540.5503.  Come in groups of 3 - 4 calls in a 20 minute time period.  Been going on for 7 days now.

faxing my cell phone

They get faxing my mother and she does not own a fax machine.  What can we do to stop these unwanted calls that wake her at all hours of the morning, as early as 3:00 a.m.

Thanks!!!