Did you try opening a support ticket, here?
https://support.brave.app/hc/en-us/requests/new
@Jiraput Just go ahead and submit the ticket. You can use the example invoice number they provide. On the Premium Support Ticket page at https://support.brave.com/hc/en-us/requests/new?ticket_form_id=360003078831, they show an example like 01234567-8910. Just enter that so the form will go through.
As a user not employed by Brave, and just an outside observer, I wanted to note the following:
The subscription terms were clearly presented when you signed up. You agreed to the charge, including the exact date and amount, and in most places that makes it legally binding. Businesses generally are not required to issue a refund if the terms were clear and you did not cancel in time.
To be honest, this kind of situation has been abused by a lot of people. Some intentionally wait out the trial or try to sign up again, use the paid features, then claim they forgot to cancel or signed up by mistake just to get more time without paying. It is taking advantage of how the system works in order to get more than what the free trial offers. That kind of behavior is probably one reason why Google has become less willing to approve refund requests. It ends up costing Brave and the payment processors money each time this happens.
Brave has still been generous in handling cases like this, even though they are not required to. But if that generosity keeps getting taken advantage of, there is no guarantee it will continue.