I am also thinking about emailing a letter to Audi UK using the contacts in the post below:
as from this thread it looks like the owner of the thread had a positive outcome.
I have ordered the isofix part (on backorder) through a repairer. Aim was to get an estimation from Audi as to when the part would become available. After more than a month of silence the part has shown up.
Now I have the part with me and 1K£ estimation for the work ... My insurance...
appreciating this thread is more than 3yrs old, I am interested in how you resolved this in the end?
I am in exactly the same situation here - Isofix mounting plate was attached to the child seat Isofix bracket (when I went to remove the child seat to clean it) and totally floating...