N300 WiFi Range Extender: The extender fails to connect to new WiFi, but shows Old WiFi

Hi, 

I recently changed broadbands. I had the extender connected to the old wifi (PLUSNET) but it is now obviously no longer in use. I have tried to connect the extender to the new Wifi (XLN For Small Biz_1ZIB), and it supposedly does connect (since the green light stops flashing whilst connecting it). However, when i then try to plug the extender in my room and use Ethernet cable to connect it to my PS4, it shows that the connection has failed. Moreover, the extended version of my wifi does not show up on neither my phone nor my PS4 (as you can see in the picture i have attached. What is quite weird is that the old Wifi's name does show up in the list of connections eventhough the router is not plugged anymore. Has anyone got a solution ?

Regards

Denis