There are a couple of reasons you could see a charge:
If you're on a paid subscription, it will renew monthly or yearly depending on your billing cycle.
If you added a new team member to your plan, you'll see a new charge for every new member.
If you have more than one team, and you're the administrator, you may be charged for a new member that was added to any of the teams that belong to you.
To check, switch between workspaces and see if any new members were added.
Contact us at hello@simplified.com to fix any other billing issues.