I used a free trial by subscribing to Trello on July 14th, 2022 (Korea)
After the free trial period, I decided to not use Trello but forgot to cancel premium billing.
I realized that I was billed 13.75$ today (August 14th, 2022. Korea Standard Time)
Since I do not wish to use Trello, i would like to ask for a refund of the service.
Welcome to the Atlassian Community!
We're not Atlassian, we can't help you with this. Get in touch with them by raising it at https://trello.com/contact (select the last option on the page, the others are documentation or will bring you back here)