Is the LED indicator of your Wi-Fi Extender PLC adapter (or Extender) red? It is probably not communicating properly with the PLC adapter connected to your b-box. You will have to reset your Extender and PLC adapters, and then resync them.
Choose your PLC adapter Wi-Fi Extender (or Extender). Does it have 2 or 4 LEDs?
Your device has one or three LEDs? It is not a Extender but a PLC adapter.