ESA Transfer to UC/ WATERSURE

Our severely disabled son recently transferred from ESA to UC and was quite straightforward as he is very disabled . However I hadn't realised when he was put on it originally that it wasn't like the DLA in that he would not have been eligible if his funds had not been as a result of compensation for medical negligence at birth. To ensure that we could demonstrate his eligibility I had to show his paperwork -just as I have to submit it to the Court of Protection each year.
Previously when we moved to last house and he was a child, I was told he was not entitled to have our water bill reduced as he was not on an appropriate benefit but after he turned 16 and started ESA I realise now that he would have been entitled to to have our water bills capped then although they were not as high as they might be. The Water Sure scheme is to help people who have a high use of water such as our son who is doubly incontinent and has a lot of laundry and needs daily baths or showers.
We thought after our move to our current home in 2019 that he was on Water Sure as the local water company set up a direct debit at a fairly low rate but recently discovered that although we signed up for their priority register - to ensure they would deliver bottles of water in an emergency situation- they had not explained about Water Sure eligibility.
We are now asking that they backdate his start date as in 2023, they stopped taking money direct debit and said they would get back to us which they did in 2025. We were instructed to investigate a possible leak which we did and then received our first invoices since 2020, totally an enormous amount which was much higher than the figure we had been expecting when we had spoken to the company representatives previously. With the pipe leaking underground, no raise in the direct debit, no invoices and false reassurances, we are now at the first stage of a complaint process.
Wanted to alert people to the possibility of having water bills capped if need a high amount of water due to disability and the risk of jogging along thinking water bills are covered by direct debits when your water board may not have checked your meter. We had not been checking ours as it is not very accessible but realise we may need to ask someone else to help by doing so after they remove the rainwater, leaves, gravel and sludge which hid it when we moved in and could not find it.