If you have just seen more than one month deducted together, here is what most likely happened.
When an auto-debit does not go through, for example a card expired or there were insufficient funds, the missed month stays outstanding. On the next successful attempt, the outstanding month and the current month can be collected together, which is why you may see a larger single charge.
What to do:
If a payment failed on our side or you were charged incorrectly, we will sort it out. We would rather you tell us early than worry about it.