I recommend you to open the ticket with Shopify merchant support team.
Hello, @LaofLa. Welcome to the Community! Thanks for reaching out about this; I understand your concern.
The 14 days of free trial time begins on the same day you open your account. If the account is not closed before the trial time expires, and a billing method is entered, subscription charges are collected every 30 days as explained in the Terms of Service (Section 14). Subscription fees are not applied by usage, I’m afraid.
How long ago did you start your trial? If you are still within your 14 free days, then the charges may have been for something else. Most often charges within this time frame tend to be from apps, domains or themes. Do you recall if you purchased any of those? You can view your invoice(s) with the details of the charges by going to ‘Settings > Billing’ in your admin.
Either way, we are more than happy to discuss the charges further with you, and look more closely at your invoice to clarify what they are for. We’ll need to access your account in order to do so. While we’re not able to provide account-specific support via the Shopify Community at this time, we’d be happy to continue assisting you through live chat, email, or callback. Please visit the Help Center and log in to your account to create a support request.
If you have any other questions or concerns, please let me know.