Hi, healyourself! Thanks for reaching out to us. We’d love to explain this further. To switch plans effective the same day, the system will require the full amount for the new plan. Unfortunately, any payment made previously will not be recognized as it was used to cover a different price plan.
In this case, we suggest you to submit the plan change effective on the next due date, however, you'll be using the current plan in the meantime. If you have any other question, just let us know. We remain at your service.