Hi @Htfc1 A device will automatically be registered when you've logged in and watched a programme on it. When you have reached your device limit, you can register a new device once every thirty days.
Is the option to remove the device showing in device management settings on the app?
@Htfc1 I tried calling there but missed you, the system is not allowing me to remove the registered devices either so I've had to raise this with our BT TV experts. As soon as I have an update I'll get back in touch with you.