If you change to an annual plan when you still have a monthly subscription period, your payment period will not be duplicated
If you Change the payment plan(Monthly to Yearly) while subscribed to a monthly plan to an annual plan, the amount deducted will be calculated on a pro-rated basis.
For example,
Subscribing to a monthly plan
The 1st day of every month is the debit day
When you change from a monthly plan to an annual plan on the 5th
Monthly plan still has 25 days left.
Normally, a new annual subscription will result in a debit of $58.80.
In the above example, the full annual amount will be reduced by a figure that takes into account the remaining Pro overlap period.