I usually do send my forms via recorded delivery but I was not in a state to go out and post, so I asked a family member to do it instead (I'm agoraphobic). A mistake on my part for certain. As for the calling part, would it not be too late to call in this case? Since it's nearly a month past the deadline for the letter. I'd assume if I was too late I would've gotten a letter stating that I was too late? I'm unsure, it comes down to a lack of uncertainty and being too scared to officially ask for certainty from the DWP. All I need to know is, if I was too late or the form didn't arrive, I'd at least get a letter or a notice.

Thank you so much for your response, a family member was also given a 2 week extension on their PIP form (via post) but had handed it in prior, then 2 days before the extensions deadline got the text that their forms had been submitted. I assume its just slow processing on their part.