Email me directly. I read every message and I answer them myself.
Two things cause this. Give it a few seconds first, since iOS applies the block with a short delay. If it still opens after that, go back into Merit, tap the app picker, and select your apps again. iOS occasionally rotates the internal tokens that identify your selections, and when that happens the old ones stop matching anything. Re-picking fixes it. There is no warning when it happens, which is a limitation of the Screen Time API rather than something Merit can detect for you.
Merit settles your balance when you open the app, and it recalculates the whole day rather than adding increments, so late-arriving data from a watch gets picked up on the next settlement. If nothing shows up at all, open the Health app, go to Sharing, and check that Merit still has read access to steps.
Open Settings inside Merit and tap Study Mode. Anything on that list stays reachable while everything else stays blocked, and you can edit it however you like.
One limit worth knowing: if you blocked a whole category and allowlisted an app from that same category, the app opens fine, but the time you spend in it still counts against your unlock. Apple's monitoring API has no way to exclude it. Allowlisting apps from categories you did not block avoids this entirely.
There is nothing to cancel. Merit has no subscription, only a one-time purchase, so nothing renews and nothing bills you again. Deleting the app is the whole uninstall process, and it takes your blocks and your balance with it.
Open Settings inside Merit, tap either locked feature, and use Restore Purchase at the bottom of that screen. It asks the App Store what your Apple Account already owns, so it works on a new phone too. If it says nothing was found, check that you are signed in with the same Apple Account you bought it on.
Email me. Tell me your iOS version and what you were doing when it broke. Screenshots help. I would rather hear about it than have you leave a one-star review and move on, although you are of course entitled to do both.