Well tbh, whatever their reason might be to not to disclose user creds, they are behaving inappropriately without any regards to your interpersonal relationship with them for years.
So I suggest you as you have no alternatives, except to intitiate formal request at exchange to help you configure the
Router. They might ask why(@Exchange) and you have to give them the same reason:LCO Behaviour .
^Don't avoid this, if LCo doesn't extend any courtesy despite all that, then you don't have to .
So it's better you initiate a formal complaint at the Exchange under a garb of request :
"Hey I need your help to re-setup my internet and phone as my LCO is not being helpful and cooperative with me. They have denied to give me my rightful user credentials despite several request and they have changed the router password on the
ONT I brought from them without my permission....<info>...As such I request you to kindly look into this matter and take appropriate actions ASAP."
with the info and then escalate it further to
pgportal.
A minor correction to anubhav: it is '@ftth.bsnl.in'
VLAN id is 152 to 153 for most of teh bsnl LCOs(They don't change the vlan as per their choice
😛)