UC not paid, no explanation

Hi! I'm appointee for someone on UC. He withdrew some capital to pay me for some largish purchases I made for him recently and informed UC of the change in amount of savings. We went in to show what it had been spent on (laptop, medical equipment, puppy and shopping I'd done for him going back over a year. It was originally about £3200 but he paid about £400 back into the savings account). Things like the puppy were to support his mental health as he's isolated due to a severe lung condition which prevents him doing much outside the house, we spend all his PIP on health related things. No warning, but his UC didn't get paid on time, no explanation. Hadn't realised it would be an issue, wouldn't have told them if we'd thought it would cause problems as at most it'll increase his payments by a few pounds a month, it was because he looked at the rules and it said to inform them, so he did. Now he's planning to save for a bit and try and replace his savings, so what should we do and will there be a problem every time things change in future? We have always spent all his PIP on health related stuff, now he get UC, how do they know which spending was PIP and which was UC?