@zuinig
You are wasting your time (for now) with the Ombudsman. They make it very
clear who has standing to complain:
They make it very clear that (for a living person) the only person who can make a claim is the account holder themselves.
Somebody dropped the ball by failing to maintain a utility bill in the relative's name. Literally every adult should always have a bill in their name somewhere and it shouldn't have been allowed to lapse. It is a daft way of proving address but it's the only system there is.