Is there a reason that this month's payment is different to usual?

If you've made a change mid-month, it will be reflected in your next payment.

Most changes made to your membership are effective immediately and if that change affects the price of your membership, or the date you pay, a small amount will be added to your next payment to cover the difference in price for the rest of your payment month. This could be a positive or negative amount, depending on whether your price has increased or decreased, and we will email a new Advance Notice to the email address associated with your membership to confirm your new payments once the change has been made.