Hi @박제용 — welcome to Figma Forum. We don't currently offer support in Korean on the forum, so I hope it's okay that I'm replying in English.
Here's how to cancel so the plan doesn't renew. On a Professional plan, a team admin or owner can open the team in the file browser, then go to Admin, followed by Settings, and click Cancel plan. This article walks through the steps: Upgrade or downgrade your plan → Downgrade or cancel your plan.
Customer Support can look into the September 26 charge. I've opened case 2155845 and emailed you with next steps.
Thanks for your patience as the team follows up on this.