PIP Phone Assessment (IAS)

I read that IAS ‘office’ assign an assessor to us. Is the assessor who initially reads our PIP2 and then requests a GPFR (in my case), the SAME assessor who does our f2f (whether at a centre or f2f)?

BIS had responded that they don't make their internal processes public. If it matters to any other claimants, I've got the feeling that the 'assessor' at IAS 'office' who insisted I have a f2f is not the same assessor who was scheduled to do my f2f, and is also not the same assessor who ended up phoning me for the phone assessment. I also am doubtful whether it's a Health Professional who reads our subsequent letters/evidence that we send in to them, but possibly a clerical person.

My phone assessor said she had read in my subsequent letters to IAS that I had requested a paper-based assessment instead of a f2f and asked me what they had replied to that? Ie it sounded like she hadn't been involved in any of that written communication. I told her they hadn't answered me, just ignored my repeated requests.

I forgot to write in the phone assessment survey that my assessor did ask a leading question: at the beginning she said, "Could you" (as in give me...) then quickly changed it to, "Do you remember your NI number?". Thankfully, this whole world is so familiar and I'd reminded myself of possible leading questions and informal observations, that after pausing to process what she'd done, I said "it's written here" and read it out. When she was asking me to confirm the reasons why we needed to terminate the phone assessment, she got some details wrong and I corrected her, and then she read out again which was better and I approved it - I don't know if she was trying also at this point to make a leading statement or not.

My belief from experience with IAS assessors that the best option for MY circumstances is to say little (so that they have very few words of mine to twist and lie about), try use the same words I used to answer the same question from my written evidence, keep silent after saying the bare essential even if it gets awkward, and let the assessor do the work and most of the talking. In this way, they have to go back to my written evidence of my PIP form and any subsequent evidence I'd sent in. But at the same time I would make it clear I wasn't refusing to participate.

Because I'm too ill to go to the post office and a friend can collect tomorrow, I'm needing to compile a letter to the DWP PIP by tomorrow. And I just do not have the time or spare cognitive energy to search around the PIP website or my PIP paperwork to find the answers. I'm sorry but can anyone help me, please, with where I can find it written (In order to quote it back to the DWP):
1) IF the DWP Complaints Dept HAVE to reply to a letter we send them?
2) How long they have to reply to our complaint letter?
3) IAS had given me an address to use re the issues but is there a standard postal address for complaints?

I've written 2 letters for the attention of senior management at DWP PIP, have printed evidence both letters were received Guaranteed Delivery next day, and had no acknowledgement or reply to either (with more than a month having passed since the last letter).

In my letter tomorrow, I want to include these facts with a request as to why they haven't done so.