@Ianmc777
If neither of the above sets of advice work, we need to know the make and model of TV involved. As HDCP blocking normally occurs when you try to use a device without HDCP compliance; of which there are two levels, one for HD content, and a later one for UHD:-
https://www.lindy.co.uk/hdcp-explained-i460#
As Now is HD at most, you may be able to get away with a device that is only compliant with the earlier standard by not accidentally sending out UHD from the Xbox One.
Set a Payment PIN on your account so that no-one but you can buy memberships on it.
Check your bank accounts monthly for any other unexpected payments to Now.
That way you can at least nip them in the bud, while you and Now figure out whose fault they are.
