If your credit card continues to be charged after cancellation, first check whether the subscription has actually been deactivated.
Open the Post app under «My Digital Post» → «Profile» → «Widget Store». If the widget is deactivated, no further charges are possible.
If there is still an outstanding charge, it may be an invoice from the active period before cancellation. In this case, contact support and provide the cancellation date as well as the relevant invoice number.
Submit your request via the ePost Support Platform or use the support chat (bottom left on the platform).