Uc payments and pip

I've been awarded higher rate for daily living and mobility after mandatory reconsideration, from zero points at review. This is due to severe anxiety and agoraphobia. Gaining points for engaging face to face and planning following a journey along with reinstating previous award prior to a review. I'm wondering if this will be backdated to 2023 when I had a light touch review given the change in law in 2016. I had no points for prompting prior to now. My evidence for anxiety and agoraphobia, being housebound , starts from 2018 and was included at mandatory reconsideration. I do not have the report from 2023 and unsure if I can get this now? I was not asked or told I could send any evidence at that point. My universal credit has decreased by a substantial amount as of this month, along with a fault of their own regarding deducting more than 15% of standard allowance for water bill and arrears when have a scheme an payment plan in place directly with water company, they have not requested any amount from uc. I'm just wondering if I could have a substantial backpay affecting my uc, awaiting letter from pip about amount. Very frustrated with uc.