Pip review and award ended, due to late return.

Hi
I am new to the forum and never had to ask for advice before, having being a member for years and using all the online advice previously. I need advice now.
I am currently claiming PIP & ESA contribution based. Pip - Mobility high & DL standard. Esa with components of severely disabled/ support group/ disability income guarantee.
My current pip is due to run out in June 2025.
Recently I needed to contact pip for a recent copy of statement of entitlement.
Literally weeks after I received it I got a letter with a award review. Date to be received by 1 November. I had less than two weeks to complete the form, find supporting evidence (most of which I didn't have to hand or waiting for) anyway despite this, I completed the form, added lots of evidence, and supporting documentation as you always recommend we do, and posted back on 26 October. Yesterday 14 November I received a letter from pip stating that my pip award will end on 9 November 2024.
I sent the form back in their post paid envelope, do not have proof of postage, as I could not physically get to a post office and unable to stand or queue for long periods of time due to my various health conditions.
I have never experienced any problems before when sending back forms & supporting documents.
I am in a mess as to what I should do next...
Please could you offer any advice as to what I should do next.
Mandatory reconsideration or appeal? Or simply start a new claim straight away?
Grateful for any help you can offer to me at this time.
Thanks in advance

i have to say its shocking how many the do not get when not sended recorded,i think i may ask for the actual numbers of claiments who report sending form back and not recieving it,good luck

Thank you for replying.
I will definitely not get caught out again with posting things back. And will take advice to get it 'signed for post'
I have a month to dispute their decision by way of Mandatory Reconsideration, but really don't know what my chances are.
I really in this benefit, and it's a huge amount to lose just because they say it was late back.
Our postal service is diabolical in my area, and our postie has said they only work 3 day week & now start at 10 or 11 am.
Thanks again. I will take all your advice and certainly call them Monday ☎️

Yes. The letter states
"We can no longer award you your personal independence payment
We have decided your pip award will end on 9 November 2024"
"This is because we asked you to fill in and return a form to us , called Award Review - and we did not receive it on time" (form was signed and dated 25/10 & posted on 26/10

If I disagree with the decision, I can ask them to look at it again. I must do this within a month of the letter (dated 10 November) this letter arrived on 14 November

that my PIP benefit has stopped from 9 November, due to form