@tp_gandhar do a full reset of the router after removing the optic cable .

I have installed v .1.13 and have not faced any issues but before updating to v1.13 do install v 1.12 which will be there in the zip file.

Yeah finally, but i couldn't understand why didn't it work when i cloned the mac address of previously working isp modem

I am not sure but i think there was some issue with the mac address as the Mac of my isp provided modem was xx-xx-xx-xx-55 but in their website where we check usage it showed xx-xx-xx-xx-5e. So when...

Got ISP to setup the router. He added the mac from TP link. I think there was some issue with cloned MAC.

Okay thanks alot for taking all the pains. ISP is mot helpful at all. Lets hope tplink release some firmware update to resolve this issue.