Spoken to BT today.
Text chat guys says that the switchover didn't happen 'fully', that there's been a mistake and I should call cancellations to sort it out.
Called cancellations, and the guy tried to sell me a load of **** before saying he was cancelling the broadband, and then passed me to billing department.
Billing department tell me that the account is still active because I haven't returned the hardware yet, and that I will continue to pay for it until the hardware is returned, then I will get a refund, if any is due!
Utter tosspots. Service ended on 31st May and I have 60 days to return the hardware, I have it here in writing.
Still on the text chat line with 'Shyani' who thankfully tells me they have spoken with their manager, opened a complaint, and got it sorted.....proper bill on the 25th July.
Although, plot twist, when I saw the upcoming DD notification from Starling I immediately cancelled it, so probably going to bounce, which will result in more fun and games.