How to cancel a Colissimo package that has already been taken over by the post office

Hello, like many of us, I was scammed by a fraudulent buyer! My package was posted yesterday, and is therefore already with the post office. The person at the counter gave me the following number to cancel my shipment: 0972721213. Unfortunately, I can't get in touch with an advisor because they "don't understand the number" of my package that I'm listing! I've made a complaint through the Colissimo website but haven’t received a response yet. The package is supposed to arrive at its destination tomorrow. Does anyone have an urgent solution?? Thank you in advance.