Poppyred, my comments are general and not directed at any specific poster.
As for missing letters, some possibilities?
Letters lost in post?
Letter gone to wrong address?
Not confident using technology, a phone call to DWP asking about the missing letter, checking personal details, including DOB and address, would set things in motion. Citizens Advice will also offer support, if one doesn't have the confidence to deal with it.
It turned out that a few people, who didn't receive vaccination letters, hadn't actually informed their GP surgery of their change of address, but still complained about not receiving an appointment. It was their responsibility to inform of change of address.
For example, I'm shielding, but my vaccination appointment letter never arrived, despite all my details being kept up to date. I knew I should have received one, I didn't mess about and chased it up. It was my responsibility, no-one else's.
Before I'm accused of being sanctimonious and critical, suffering from chronic ill health and often having brain fog, I do not find these tasks easy, but I try.