Re: ESA Marker against my name

Re: ESA – Markers against my name
On Friday a wonderful helpful lady told my cousin who rang the Health Assessment Advisory Service call centre that it was in my interest to know that there is an ESA Marker held on me which has been preventing me getting Home Visits.
To say we were shocked was a understatement and now finally after all these years it all makes sense every time having to go through all the same stress and tribunals Doctors letters and letters from family/friends/neighbours every time asking for Home Visit with no explanation as to why I was getting denied home visits due to agoraphobia Fibromyalgia Chronic fatigue stress and depression
Since February 2019 I have been this merry go round again with the ESA who have again repeatedly ignored Dr’s family/friend/neighbours’ letters asking for home visit and then ESA asking why I did not attend appointment. My reasons were accepted by a Decision Maker in April.
However, out of the blue 5/7/19 I received another letter from Centre for Health and Disability Assessments in Marylebone London which is approx. 15 miles away with two working days’ notice I was distraught and is a big worry and stressful not knowing what is going to happen to me until this is sorted out.
Had it not been for my cousin taking control to ring the Health Assessment Advisory Service I would still be in the dark had it not been for this helpful lady I would still not know the real reasons of why I was getting denied a Home Visit? She told my cousin this is the reasons because there is a marker against me to say I am a risk to those who attend a Home Visit and believed I had a right to know.
The lady asked did or has anything ever happened that would or could warrant this my answer is no nothing that could warrant this a permanent marker without my knowledge.
How do I make a (SAR) Subject Access Request as I feel this is abuse of power?
I want to Who and Why and What are those reasons and how long and when did this happen.