Don't wait for another transaction.
Steps
If possible, temporarily block your card in the app and immediately call your bank's call center, clearly stating that you have received an "unauthorized transaction." Request that your card be secured and that you file a complaint, obtaining a reference number for your complaint.
Keep a copy of the transaction details, including the transaction time, amount, and merchant's name, but do not send a screenshot showing your full card information.
The Central Bank allows you to submit complaints to the bank through its call center or official channels, and the bank is obligated to provide you with a reference number immediately or within a maximum of two business days.
The figures, fees and limits in this answer vary by bank and change over time — confirm them with your bank or the official source before acting.