This is potentially due to when your new direct debit was set up.
For example, if it was set up and started in August, it will be calculated across the next 11 months. If it started in September, it will be spread across the next 10 months. All direct debits will be calculated to be paid by 30 June 2023.
Next year, for all direct debits already set up, the calculation will be based on a full year (12 months).
Please note - there is no charge applied for paying by direct debit.