Thank you all. My screening mammogram report shows a stellate lesion and I think what @primek says the biopsy is just to find out the type for finding the right treatment in my case.
I think that, as @primek said, this is a technicality and some legal advice is required. The Ombudsman is a good point to start (saying that, I have never contacted the Ombudsman for anything so cannot comment on the pros/cons).
Personally (and I know this has no legal standing), I would take it from either the screening date, or at least from the date that your screen is read and deemed to be recallable as it is at that point that something has been noted.
