Don't worry. This is due to the trial month. You haven't had to pay anything yet, and the mail informs you that after the trial month, you will automatically have to pay to extend, i.e. the actual premium will start.
It is just the info from the system that your current premium, i.e. the trial month, will soon expire and then the next premium, i.e. the real one for e.g. 12 months, will start.
Only then you pay. There will be no double booking.