Are you on fiber? The set up in some cases involves 3 pieces of equipment:
1. A white Nokia modem (aka ONT) for the fiber line
2. A black modem being fed with both an Ethernet from the fiber box above AND coaxial line (which is actually split to feed the phone modem below)
3. Phone model being fed by a coaxial cable
I ask because this set up does not support VOIP and the alarm company phone number may be a digital number with an IP network set up (very likely as most companies do this when they need lots of phone numbers). If so, maybe ask your alarm company to assign you a non VOIP number. Another way to test this is turn off your cellular radio on your phone (assuming you have an iPhone). Then enter your cellular menu and enable “wifi calling” and attempt to manually call the alarm number. If it fails, then you know VOIP is the culprit.
good luck.
We are still coax to the house, split to cable modem and Cox provided Arris modem which provides dialtone and such. So basically option 3.
I'm not using an iPhone (prefer the customization options with Android), but have tested the number using my Google Voice number from the app on my phone and it rings through to the alarm company and gets the modem answering tone. I'm also able to call the number without issue from my work computer's Skype connection. The only time I get the error saying that the number has been disconnected is when I dial it from my Cox connected phone.
Can you dial and connect to any other telephone number via your Cox-connected phone?
Cox provided Arris device providing dialtone to the house
Not to be a pain, but could you upload an image of this device?
To answer the first question, I've only tried calling a few numbers (local and long distance) and everything went through. The only one getting the disconnected error is the one to the alarm service, and it had been working for over 10 years until April 6.
Here are the pics of the Arris device used for the phone service here. I tried a manual power cycle of it (including removing the battery and letting it sit for 10 minutes), and I tried using the reboot option through the Cox website, but nothing changed.
https://photos.app.goo.gl/HR6LgQYnmCr4hJDv7
https://photos.app.goo.gl/NEVjRaZRj7bpZfGs7https://photos.app.goo.gl/QjtY4CaVDJ3FQLFk9
