I believe that BT Wholesale were contacted and asked to look into this. The lady on the phone said a home visit would be the last resort but it may be fixed by then.
As you've had problems with the Youview box since the beginning I'd be inclined to think that it might be the issue and a replacement unit is required.
I had problems with the UHD box and eventually after 2 swaps went back to the standard , more reliable box. Not an option for you with a UHD package though.