Cancelling a subscription on the member detail page does not automatically forgive current payments owing whether they are set to Cash or Card. The system will still try and collect on the payments you see in the 'Overdue' tab of Payment Report.
If for whatever reason you do not want to collect on any Overdue payments you can use the context menu to select 'Record Cash Payment' or 'Record Credit Payment' and then select 'Comp' as payment option in the modal. This will not charge them but clear the payment from the system.
Deleting a member is also not a solution for forgiving a payment which is due.