T46s Need help proving to ISP that they have caused a fault

[simonl]

Hi Everyone

I'm looking for some help to prove that changes our ISP made to our router is causing problems with our phones.

We have had 26 x Yealink T46s phones for over three years now with no problems what so ever, these phones were a God send during the pandemic.

But since our ISP had problems updating the SSL certificate on our router and needing to get Cisco logged in to rectify it, we have had nothing but problems.

The problems are:

1. One-sided audio half way through a call - both sides can be heard on the VOIP providers call recording feature, but we cannot hear the caller.

2. Busy lamps continue to flash on all phones after a phone has picked up the call rendering it impossible to use the menu buttons to contact other extensions.

3. Certain phones not ringing on incoming calls.

4. Random phones stop communicating on the network, even the back-end web interface is not accessible for a minute. This occurs in a pattern, 10 minutes, 10 minutes, 20 minutes, 10 minutes, 10 minutes, 20 minutes etc.

5. All phones showed no-service one day, but plugging a phone into a router at home worked perfectly. Turning the router off and on resolved this.

Our ISP is blaming BT our VOIP provider, so to disprove this, I have set up a 4G router with a couple of phones connected. This has worked faultlessly whilst all the other phones on our office network have still played up.

So I'll be going back to my ISP with the result of running on 4G, but I am worried they will still try to wriggle out.

With the above symptoms, are you able to suggest what's causing this?
I have asked them to check SIP SLG is not active and they confirmed it's off.

Any help much appreciated.
Simon