Hello @Elba Alján, welcome to Figma Forum!
We don't currently offer support in Spanish on the forum, so I hope it's okay that I'm replying in English.
I'm not able to access billing details from this public space, but I've opened a ticket on your behalf with our Product Support team so they can look into the seat change and clarify what happened with the Collab to Full seat upgrade. Your case number is: 1881871, and they'll follow up at the email tied to your Figma account.
If you haven't already, I'd recommend checking your current seat assignment and downgrading to prevent any further unintended charges: Upgrade or downgrade your plan → Downgrade or cancel your plan.
Please keep an eye on your inbox for next steps. 🙏🏻