Some subscribers may have signed up the 50% off for 3 months, and that's why they were paying the $5 amount.
Right now, the current discount is $7.70 for 3 months. Once the promotional discounts expired, you're billed the regular price for your subscription, which is $15.
I suggest checking out the updated details through this link: QuickBooks Self-Employed plans and pricing. Then, you can sign up for a new account and enjoy 50% off for 3 months.