NEC TOPAZ attendant message and indicator light stays on

[Zero6]

Hi all,

I have a phone model: IP2AP-12TXD TEL2(WH), where the indicator light stay on in right corner above and when you dial the number internally, you will hear a message no attendant is available.
All the other phones are working normally and the main phone receives all call, it is this ext 601 which has an issue

It is connected to a NEC Topaz.

Does anyone have an idea how to disable the light and the message playing when you dial the extension.
I tried DND and clear all messages, but it didn't work
I have attached a picture of the phone

Thank you in advance