DLA TO PIP

Hi I'm new on this

I'm on dla care middle rate & higher mobility rate.
Through the letter box came this white envelope inside was “PIP2: How your disability affects you”
I knew this day would come from my dla being replaced. But seeing it gets me thinking of all kind of things it doesn't help my anxiety depression.
Anyways I filled it in with my conditions also sent evidence of what I suffer from. GP done a letter to them aswell. So sent it off with 30 pages of records etc.. in August.
Last week I get a letter back saying
We're writing to let you know that we've asked for further information
From people involved in your treatment or care.
This has made me very stressful & upsetting as how can they ask for more. When I sent over 30 pages.
It's like they don't believe me.