Sounds like your system lost its programming so now the voicemail ports are just like extensions, they are ringing and picking up. And since the voicemail doesn't know where the phone systemn is, it just transfers all calls to the lowest numbered extension (10)
A hard reset will clear a consumer set pass code, unless it is stolen, reported stolen or the code to open has been entered wrongly 4 times. Then it becomes PUK/SIM locked. EXCEPT, now I looked it up, this is a home phone!
https://downloads.avaya.com > css > documents
PDF
Replacing this function will lock the phone for further programming until reset through the telephone system. 8. If the display slot is not already used, the ...
arrow keys to locate the option Call Settings.... arrow keys to locate the option Show Phone Screen. arrow keys or press the On/Off soft key to change the setting. number and name.
Power surges damage electronics that power up devices. The surges push too much current into the units sensitive controllers and thus damage the units beyond repair.
As a system ages, it declines just like people and thus tend to break down gradually. Power surges just make electronics go faster down hill.
On most phones, a red light indicates a message in voicemail. You need to press the MESSAGE button and follow the instructions on pages 4 and 5 of this reference manual.
https://downloads.avaya.com/css/P8/documents/100130184
Have you tried to retrieve any message? Sometimes another extension will set the MW light on inadvertantly.
Calling the VM won't help but if your retrieval attempt keeps ringing it will be a phone somewhere within the system. FIND IT & Answer the call at THAT extension and the light should go out. NB sometimes there can be more than one in Queue. Panasonic stack up to 8.
This is done via the Avaya Manager program on the PC that is administering it. The Main system Password can be hacked and reset but it takes special equipment and training.
If you can't get in normally, I say time to get an onsite tech.
