@Viribus Unitis - Re;
I noticed an additional charge for team members who were accidentally added
and
I'm concerned about this unexpected charge
It sounds like additional users being added caused additional charges, which would be expected.
If this is the case, you may want to review your team invitation settings to ensure that only admins can invite people/increase your license count.
Here are some links on the topic:
Contacting Support for Billing Questions
Since you have a paid subscription, you can direct your question to the support team who will be best suited to determine exactly what has happened and to dispute any charges.
You can open a Miro support ticket by following these instructions:
https://help.miro.com/hc/en-us/articles/360020185799-How-to-contact-Miro-Support#h_01F010RXA0E1S9C0WFQYX75R6C
After you have selected Contact support from the Learning Center, select Billing & Subscription → Billing & Payments / Other.