PIP downgraded from enhanced to standard

I had an award ot PIP at the enhanced rate, which I have held since 2011. My award was until October 2019, but in August I got a letter saying it was time for my review. I completed the forms and put all of my conditions. I have a severe heart problem and very severe arthritis in both knees which means that I cannot stand for more than about thirty seconds and cannot hardly walk at all without help, and even then I have to keep stopping as I get very out of breath and am in terrible pain. I was called for assessment and at the meeting I got very upset as I was with my daughter and talking about things like incontinence and not being able to do very much in front of my daughter was very embarrassing, plus I am so worried about my heart and the possibility that I will die soon. The assessor was very nice, but her report bore no resemblance to what happened in my assessment. She said in the report that I was pleasant and not in any way distressed, but that is blatantly untrue and when it was time for her to look at my mobility she said for me not to stand up as she could see I had difficulty, so she just asked me to lift my arms. Her report said that I have normal mobility in my hips (I do NOT) and no reduced power in my legs (I cannot even step up a kerb) and that, although she didn't see me walking "on the balance of probability" I could walk more than 20 metres. She awarded me 10 points which means that they have taken my enhanced PIP off me and I now have to return my car to motability and without that I cannot go to work, as getting in a taxi is really hard for me. I asked for a mandatory reconsideration eight weeks ago and have just heard today that they have turned me down. I am frantic as I NEED my car - I only work part-time but I need that contact as otherwise I would never go out. I am beyond upset - I cannot afford to buy a car and I just don't know where to turn. What can I do?