Spreading your usage over the year and paying the same amount each month means that you can normally expect to be in credit at certain times of the year. You often build up a credit balance during the summer months, meaning your account will be in credit. It’s a good idea to leave this credit on your account going into winter as this will cover your increased usage.
If you think you are paying too much, or you’re building up a large credit balance then you can request a refund here. Don't forget, whilst your account is in credit you will be earning 3% interest reward too on balances up to £1000.