Benefits are such a headfuck. I used to do welfare advice, in an Unemployed Centre, 20+ years ago, and
then it was possible to learn about the different sorts of benefits, and understand them and how they're calculated, and challenge them if an mistake's been made. Nowadays, I find, I haven't a hope in hell of understanding how our UC is calculated (and I'm quite educated and numerate, god knows what chance you stand if you're not, or if English isn't your first language, you really are at their mercy). Or the deductions they take every month to pay back an overpayment I've no hope of understanding why we owe in the first place. My husband earns varying amounts each month, or is sometimes out of work, he's self-employed, formerly as a Ltd company, but now as straightforward self employed sole trader. This added a huge extra level of complexity, I got the impression the benefit people didn't understand it themselves. The best person I spoke to was at Council Tax, although we missed out on CT reduction by having an annual income of about £100 too much
HMRC are much the same, according to OH, they seem to pluck figures out of the air, one week you owe them, the next they owe you, and again, they don't seem to fully understand their own rules themselves.