Best answer by woz
I'd guess what's happened here is as follows, but there may be other explanations...
My guess is that you moved into the property which was already supplied by Pure Planet, that made you a "deemed customer". As with anyone else in those circumstances and with any energy provider (not just PP) you would have had the option of staying (with PP) - (probably your best choice but I would say that) or switching to another provider. You didn't switch.
PP is app only, you could have downloaded the app and joined when you moved in but maybe you didn't know.
If you now join PP through the app you then set up a direct debit to pay ongoing bills and I guess they can add the previous usage to your account and arrange payment, or you can arrange payment as a one-off <-link if you decide you don't want to stay with PP, but if you don't, and want to switch away you'll still have to pay for the energy you used from when you move in to when you switch to someone else.
As I said it's a guess but without more details and history who knows...
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