Cancelling a transaction

Hey, I was buying a steam code and the guy put it as sent and received. But I have not received it and now he says that he has sold the code on another site. Is there a way to cancel this transaction? I can pm my order ID. Thanks!

please do NOT rate the Seller If the seller delivered a defective or inconsistent item, please open a dispute by clicking “I have an issue with the item I received” and describing the problem in the resulting text window. Be sure to attach any screenshots that support your case.

But there isn’t any screenshots that I can provide, the text chat is my only evidence

ask him for write/give your new code if that your problem, if he (the seller) wont, just dispute and go to team support