Do Credits Roll Over If Not Used?
Yes. Unused credits roll over to the next billing period, for as long as your subscription is active.
On a 100-credit plan with 30 credits left at renewal, your balance goes to 130, not back to 100.
Cancelling stops it. If you cancel, your credits stay usable for 30 days from the day you cancel, and unused credits are removed after that. Resubscribing later gets them back: ask for a human agent in the support chat once you are on a plan again.
Your current balance is in the top bar of the dashboard, and on Billing next to your plan and renewal date.