PIP query

Hello, just a query!, i was put onto Pip, after being on 'DLA' for many years (I have Mental Health issues), also Arthritis, which i got the Mobility on DLA, my assessment was 'paperbased' and not done by a Medical professional, I was awarded '11' points for 'Daily living' and '4' for mobility, i asked them to look at it again, they reduced my points to '8' for 'Daily living' and nothing for Mobility (even though I have my diagnosis on Medical files), they are saying that because I didn't provide evidence, that's why!, i've now lost my mobility component and the mark for 'anxiety' they have removed (struggled to get on public transport), as they said I am able to go to a row of 8 shops two minutes away!!, I have lived in my home for 26 years, so know the area well!, also won't accept that, because of my Arthritis (Spine, both hips and knees), at times I can't leave my home, as I live on the top floor of a block of flats and have 30 stairs to climb, they have told me that doesn't mean I have 'mobility' issues??, I need some advice please!