I am surprised by the response of your advocacy worker because no one expects them to give medical evidence. I don't know how much contact you have with them, but surely they can write about what they have observed of your difficulties that are relevant to the PIP criteria. If they didn't know you at the time of the claim, then anything they say now won't hold much weight.
I understand your frustration about being asked for evidence from Jan 2019. They've made the request - so you would be unwise to ignore it. However, you can do as you have done here and write a couple of paragraphs about why you had little contact with a GP when you moved three times and online appointments were not available. I would hope the Tribunal Panel would understand that. There are thousands of people in the same position as you. You cannot provide evidence that does not exist, so a short letter from you responding to the request should suffice.
BIS
Nothing on this board constitutes legal advice - always consult a professional about specific problems
