Severe dissability premium

Hi poppy you. Seem to be quite clued up on sdp, I wonder if you can advise me please. My daughter stopped getting carers allowance for me on 9 July 2018, should ESA have put up my enhanced premium then to the severe premium, since then I've been entitled to the sdp, but didn't no about it, so I only started getting it when I claimed it 27.3.2025, my friend told me that he dad had been awarded sdp without him actually claiming it ,he just received a letter saying they were back paying him 22k , and when I did put in for sdp the man on the phone said I could be in for a large back payment, so why haven't they given me it, all they've said is I can request a mandatory reconsideration, is there any point to me doing this