Crashing the network by dialing a number - somewhat solved

I am somehow crashing an entire network, with the symptoms of a network loop.
somewhat crazy but if i dial the extension to extension its fine.
if i dial from internal extension to DID of internal extension the phone call picks up
and crashes everything, and by everything brings everything on the network down as if there was a network loop
the last thing i see on the logs is

SIP/VI-TRUNK-OUT-0000000d answered SIP/205-0000000c
– Channel SIP/VI-TRUNK-OUT-0000000d joined ‘simple_bridge’ basic-bridge <291d9773-3cd5-4369-a367-159ff1ffe01e>
– Channel SIP/205-0000000c joined ‘simple_bridge’ basic-bridge <291d9773-3cd5-4369-a367-159ff1ffe01e>

so im dialing an extension/did that has nothing on the other end, so it should goto voicemail. which it does when i dial the extension, but if i dial the DID it somehow acts as the line picks up which i am assuming is the Simple_bridge"
and crashes the network

any help on this would be appreciated. I am remote and it is a production network so i will have to wait till late tonight to figure out what is going on.

Just a little update this was caused by an internal caller calling another by their DID
my setup is for a assisted living center so each extension will have there own DID.

so the call was being routed out to our carrier instead of staying in it would ring but once voicemail hit,(even when VM was disabled the call still picked up somehow) the network would crash.

I am trying to find more information on a loopback trunk i believe i have it set up correctly. i just need to get the dial plans right. to where the dial a number thats local it stays internal and not out to the trunk

I thought everything was resolved but this peaked back up.
in terms of migration with the old PBX still in production for many extensions while testing, everything worked fine except when i called from new PBX to old PBX it would give " all circuits busy, with a 503 error. but the other PBX didnt show it in the CDR as even touch it. i then tried it reverse, where the Old PBX called a new extension on the new PBX and the call goes through, if you pick up , it goes dead and network loop is created.

Now you are starting a to spill the beans a bit…

You have two PBXs on the same network. How do they talk to each other? What phones are you using? how are they registered?
Happens from all phones? Describe please “the crash”.

With no details, or logs it’s pretty hard to find someone here that will be able to help you figure out whats wrong.