Hi @HAPPY-GO-LUCKY
I really do apologise that you were charged for calls made on teams. You are charged for calls made on Microsoft Teams based on whether the call is to another Teams user or an external phone number, and what calling plan you have. Calling other users on Teams is typically free and uses data but calls to external phone numbers (landlines or mobiles) can incur per-minute charges that are either deducted from a pre-paid Communications Credits balance or billed as part of a calling plan. To avoid this in future you will need to set your bill CAP to £0.
To set your iD Mobile bill cap to £0, log in to the iD Mobile app or online account, go to the "Bills" section, find "Manage bill cap," and move the slider or input the value to £0. Confirm and save the changes to prevent any out-of-plan charges.
-Owethu