Hey @SonaP — welcome to Figma Forum and thanks for taking the time to share what you’ve encountered.
I wanted to offer an explanation of where these charges most likely comes from. On the Professional plan, giving someone edit or Dev Mode access assigns them a paid seat — a Full seat for edit access, a Dev seat for Dev Mode. When seats are added mid-billing cycle, they're billed separately and added to your invoice on top of your base plan, which is the usual reason a bill goes up the way yours did. For more on how added seats are charged, have a look at this article: Manage billing on the Professional plan.
For a breakdown and options specific to your account, the Product Support team can look directly at your invoice and seat setup. You can reach them by opening a ticket through the Support Hub.
Your point about a clearer warning before an access change triggers a charge is fair feedback — I'll pass along your experience to the appropriate team.
If you run into trouble getting through, or any questions remain, let me know and I'll be glad to help. 🙏🏻