Nick here from Shopify.
In the instance that your trial has ended, you won't have to worry about charges (even from apps) because the store is the same as canceled in this case unless you sign in again and pick a plan (everything will be like it was also). So no need to pay the subscription of €29 to re-open it here, just to be aware that when you do re-open it, it could potentially charge you for the app.
The other thing to think about, is if you were still on trial, did you add a credit card to the store at all? Normally if you are still on trial, you wouldn't have added any card details to the store profile and wouldn't be able to be charged for anything.
If you have any other questions about this or anything, let me know!
All the best, Nick
Ah ok, it might be worth reaching out to the support team directly to see what exactly is going on to be sure in that case. You still wouldn't be charged in this case, but the trial would not have ended if you had picked a plan and added your card details so that seems very unlikely.
You can reach the team by phone or live chat from the link here.