This brings back memories.
After my divorce, I decided to rent rather than rush into buying a place and I think I dropped on with the UK's only decent landlord!
Anyway when you move into a rental here you have to basically take the incumbent supplier for the first month or so before you can choose another one.
As it turned out though, the current one was offering the cheapest rates so I stuck with them. For 9 months whereupon they went bust as well.
The new operator came onboard and it took another three months before I was on their system. 6 weeks later I moved out of the property but had the lease for around another 5 weeks or so.
Then the fun started. The landlord couldn't get the new tenants signed onto the gas and electric because it was still in my name (despite having told them I'd moved out).
Then they decided I owed almost £3,000 for roughly 3 months of energy, more than half of which no one was in the property.
Then they told my ex-landlord what I allegedly owed.
Then they denied having, or even needing to have, a DPO.
Eventually I emailed the CEO and within 10 working days, they acknowledged the problem at their end (I had monthly meter readings despite them being allegedly smart), informed me that the outstanding bill was actually £110 (which I'd still have argued was wrong) but as way of an apology, waived it.
Their DPO tried to deny they'd discussed monies owed with my ex-landlord, despite my having an email from him where he told me the exact amount (arguably no proof I hadn't told him it first, of course) but in the end I couldn't be bothered to carry on arguing.
But it's so concerning - had I been old and/or vulnerable, that would have been potentially dangerous. Their handling was just aggressive and shitty.