Wifi Extender Not Working

I have a Netgear AC1200 Model Wifi Extender that I’m trying to connect to. The thing is is I have used it before, last year with a different wifi than I have now. It worked perfectly fine and connected with the same wifi password as the actual wifi.

Now this year we switched internet providers, we have reset the extender, tried every possible password we could think of. It comes up as our current wifi name _EXT which seems right and like it’s connected to the wifi, but when we try the password it says it’s incorrect.

Does anyone know how to fix this problem? I’m very stumped because I know it works!!!