@Marieosmond did you just made a payment to the old plan?
What you need to do is to make a change of plan using the option "Change on the next renewal'. With this option the change of plan will be on your next renewal date and so it won't double charge yo. (DO not click Change plan now if you don't want to start the plan immediately. With Change plan now, PM will charge you new plan amount immediately and start the new plan , but unused days on the old plan will be forfeited. )
Also I suggest you to load enough fund for the new plan. Even you are using Pre-Authroized payments, it is better to manually load enough fund for the new plan ahead of the renewal. This will assure a smooth plan change.
