You may have activated a vehicle too soon. Vehicle activations are reset on the first of the month 00:00 UTC. If you are in a timezone that is ahead of UTC, you may have activated this vehicle too soon, and in the UTC timezone, you actually paid for the last month.
To avoid this, please look under the price which shows how long this vehicle activation is valid. e.g. “for next vehicle activation this month (valid until 1.7 01:00).