Hello @Madddy ,

Thank you for your detailed post. Range extender does not connect router's Wi-Fi successfully of the Signal Led/ Wi-Fi LEDs are off. 

Most of the time that is because of the wrong Wi-Fi password when set up range extender. 

1>Please verify your Wi-Fi password by forgetting your Wi-Fi network on cell phone first :  
Go to Settings→ Wi-Fi on your phone, Tap (or Long press  the router's Wi-Fi name  →Forget / Delete the network 
Please reconnect to your router wifi, and it will ask for a password, will it accept your router password?

Then factory reset range extender and set it up from scratch.

2>  WPA2-PSK(AES) wireless security is recommended on Wi-Fi router, do not set up Mac filtering  or Whitelist or other advanced settings that may affect the range extender 

If the concerns persists, can I know the model of your Wi-Fi router, and please share a photo of the Wi-Fi settings on router. 

After set up, check if the Signal or Wi-Fi LEDs are On or not, later  login Range extender Web page, go to settings--system tools--system Log, save the log and send the log file to us.