How DO I change the Billing Date from the 21st to the 25th or the 1st of the next month?

Far as I know, you can't change payment dates as you are charged on the anniversary of when you first took the product out....missing a payment would reset that presumably.

Only way I know is to cancel the product and then buy it again on the date you want

Hello, My name is Jesse. I'm an Independent Advisor and a member of the Microsoft community and I'd love to assist you today.

The only way around this is to let it expire again and renew it on your preferred date.

Hope this helps.

february 21st or 25th are the most likely dates

If I had to guess I would guess the bill date on your account is the 25th of each month but your autorenewal date for your last subcription was on the 26th so you were billed for the current month of service on the very last day of your service month. So
that charge was for your last month of service (10/26-11/26).

It's likely because the billing and renewal date are different. The renewal date only effects the current subscription, but the billing date is always the same.

So, in this instance, her renewal date was the 22nd. If you let the subscription lapse, and decided sometime in the future it should be turned on again, but say on the 1st of the month. It would charge when you first purchased it, and then the next month
it would renew on the first. The charge, however, would not process at the same time unless the billing date was also the first. If the billing date is more like the 15th, it would hold as a pending charge until that date hit.