When living in the UK I quickly learned never to give those guys direct access to my acount such as via a Direct Debt: without it, their mistakes are their problem to solve, with it their mistakes are your problem to solve.

Get invoice; check it; call them and ask for proof you spent 3 years worth of power consumption in a single month and pointing out that their meter reading on that invoice is totally different from what the meter says; get an updated correct invoice.

Compare that to the chain of problems that's the result of your bank account going into overdraft by a couple of tens of thousands of pounds...

It's not even that they're doing it on purpose: it's just that they employ people for peanuts to maximize their £££ in profits hence mistakes are far more likely and if they're not the ones bearing the costs of such mistakes (and given the laughably corrupt UK Regulators, they're not) they won't spend a single penny to put in place procedures to catch those mistakes.