Let me route you the best support so this will be taken care of the soonest.
It's possible that the discount on your plan was already expired that's why your subscription fee increased. To verify this, I'd recommend contacting our Customer Care Team.
One of our representatives will pull up your account in a secure environment and review your billing history. Here's how to connect with us:
Select Assistant from the top bar.
Enter "Talk to a human" in the search bar.
Enter a brief description of your concern, then click I still need a human.
Did you purchase your account 3 months ago? Your discounted rate is expired and you have to pay the regular rate now. You may open a new blank QBSE account with another email address to get a longer discounted rate and migrate your data manually from your old account if required.