get proof of postage

i would just like to say when sending documents or forms to dwp send by some sort of tracked or recorded delivery.
my daughters review form for pip arrived around the 20th of october it was posted on the 23rd and was signed for on the 25th. pip review wasn't due until 14th of november but as it was basically a no change ticking operation which we backed up with up to date evidence i assumed that was pretty simple and it allowed us to get it to dwp with plenty of time. however today had letter saying pip review form not received after a conversation with dwp they said they would extend the return date by 2 weeks as i had sent it and could prove it. this they said allows them to chase up why it has not been scanned. someone from dwp did phone me an hour later to confirm the 2 week extension just in case on the 14th they closed my daughters claim and also to voice there concern as to why they can't locate form. i was told by this woman that this was only being done as i had proof of delivery with a signature.

so my advice is please please when sending anything send it by recorded or next day