Starting from the point in time at which you order a monthly plan, you will receive your first invoice/bill +/- 7 days after activating your new monthly plan.
E.g. Did you order your monthly plan on 16 November? Then your invoice/bill date will be on 24 November. As a result, you will receive your invoice/bill on or around the 24th of every month.
On your first invoice/bill you will also pay the monthly plan for the next month at the monthly price. This explains why the amount is higher than expected.
So on your first bill/invoice, you will be charged for …