Used points for a stay, but my card got charged anyway

Booked a Holiday Inn Express by the London airport using points before my flight home. Just noticed they still charged my card for the full rate.

When I called, they said their fraud system flagged the points booking and switched it to a paid stay without telling me. Nobody mentioned it at check-in or checkout.

Now I’ve been stuck going back and forth with them for days. Has this happened to anyone else?