Installed a powerline adaptor kit about 12months ago to extend the home WiFi (bt) from the house down to our office in the garden as the WiFi didn't reach, don't recall exactly how I installed them, I would guess following the instructions, anyway, everything worked perfectly and our broadband was extended, the SSID of our existing router was being broadcast and all our devices connected no issues. Our broadband died the other day and we had to reset the router (well BT did remotely) and the WiFi for the office dropped out, when we tried to log back in the office WiFi, our bt router had disappeared and instead the tp link is broadcasting its own SSID.

Our smart tv in the bar (next to the office) won't connect to the tp link anymore, and obviously can't find our bt router SSID anymore

Is there a reason for it changing? Can i get it back to how it was originally? (I'm pretty sure I didn't change the SSID on the tp link when i installed them) 

Thanks in advance for any help