Martin Lewis will tell you all you need to know.
With direct debit your account should be most positive (in credit) in November (maybe around 2 months worth). By the end of March you'll have used this all up and likely go negative and this will build back up again over the summer.
If it's wildly different from this then your power use may have been wildly over/underestimated. Then you'll be due a large refund, or your direct debit will be adjusted up.