it could be through the vm, check manager mailbox password is on and not changed. look for extensions fwd or external notification on mailbox is set to premium number, check all mailbox's especially one that has no extension assigned.

smdr if turned on and not collected has a buffer, but will only hold about 100 records and will lose them if the power is off, but the unit probably is not turned on to collect smdr if it has nothing connected to the port

“I have not failed. I've just found 10,000 ways that won't work.”