First, you can ask BSNL to provide:
1. PPPOE User ID, Password and VLAN.
2. VOICE Username/Account No.(same), Password, VLAN and SIP address.
With these you can reset your ONT and configure it on your own without involving your LCO.
Second, If they ask why you need then tell them you bought ONT from LCO and he is not sharing your id password to access ONT.
You can just stick to I want to change firewall settings or wireless settings or whatever excuse you can to get id pass.
Third, If they don't want to share or annoy you or whatever then don't care about anything and stick to "I bought it so I want id and password".
1. PPPOE User ID, Password and VLAN.
2. VOICE Username/Account No.(same), Password, VLAN and SIP address.
With these you can reset your ONT and configure it on your own without involving your LCO.
Second, If they ask why you need then tell them you bought ONT from LCO and he is not sharing your id password to access ONT.
You can just stick to I want to change firewall settings or wireless settings or whatever excuse you can to get id pass.
Third, If they don't want to share or annoy you or whatever then don't care about anything and stick to "I bought it so I want id and password".