Just a follow up to this.
So I never ended up contacting O2 to say “please stop this”, I just used Wireguard to home and ignored it. Until the local Morrison’s wifi started doing the same thing but worse and I couldn’t event Wireguard round it.
So I finally just bought a domain and setup my Apache to redirect the old duckdns to the new domain.
So far this all seams to be working great.
I can only speak of on Linux. If you know the disk is bad, clone it, with ddrescue, and fix the clone. But in future RAID and backup remotely. Also, next gen filesystems like ZFS and Btrfs for check sums and self healing and subvolumes with send/receive deltas between them.