Hello BumbleBee2015,
When you subscribed to the 250M characters per month level, you paid for it already at the start of the subscription month. There are no refunds or credits, nor can you rollover characters to a new subscription month.
If you know your when your subscription started, change the subscription level towards the end of the subscription month. The subscription date is in your My Data page at
https://datamarket.azure.com/account/datasets.
The date of the month indicated for your subscription stat date is the monthly anniversary date. On that date each month, the full character balance that you are subscribed to is reset into your user account (if you buy a subscription on the last day of
a month ending on the 29th, the character balance resets on the 1st of each month).
Double-check for the auto-refill feature (for paid subscriptions) for your new subscription if you would like it enabled.
Hope this helps.
Thank you.
Microsoft Translator team - www.microsoft.com/Translator