@jimmy
From their FAQs:
If we think you’ve got more credit on your energy account than you need, you’ll be able to request the excess back as long as you’ve had an energy bill based on real meter readings in the last 14 days. To ask for your credit back, just hit the little button underneath your balance on your online account dashboard.
If you think you’re due a refund but you don’t see an option on your online account, just email hello@octopus.energy to talk to the team. (Make sure you’ve given up-to-date meter readings within the last 14 days.)
Max £500 at a time, I think.
I find it a good way of saving money – but then I’m shit with money…