- File a dispute
- File a report on that trade
They have chat support, the paxbot and you can just chat your message there about this concern which is likely a scam attempt. If you know that the transaction proceeded successfully, there's no need for you to cancel the transaction.
That bot is annoying if a new user is not familiar with it but after a few times, it's useful.
All of those: dispute, report, support ticket will take time to be handled.
I guess that's a matter of urgency if they're able to understand the concern so fast that there are some users of theirs that are trying to use their platform getting engaged into that activity.