CCabinet P7 FTTC Available from 22nd April 2014 Phase 10b 2013 309 Huawei LU7 0QE
as you can see the cabinet shown on your dslchecker results has been fibre enabled for 4 yrs. maybe it has had the capacity increased recently
I really don't understand why you have been told fibre has just been made available, as I said, cabinet 7 has been enabled since 2014. If you are connected to it, nothing has changed since then. Have a look around Mentmore and see if you can see 2 green cabinets close to each other with a number 7 painted on one of them.
Edit: @imjolly could have a reason if the cabinet was previously full.
Unfortunately, I supect that means the checker is wrong and you are too far from the cabinet to get a sensible speed.
Did you locate where the cabinet is?
cab is supposed to be at p[ost code LU7 0QE I know from my own cab that is not quite accurate just in right neighbourhood
If there is no cabinet within about 3Km or so by road from your house you are beyond the range of FTTC service.