Just to confirm:
Does your APP show up your PNR with a ticket number associated to it, or was it completely gone after you cancel the wifi?

If you have a valid ticket and booking on arrival at the airport, then it would be a denied boarding. If the ticket number is gone, then the airport's agent is right, they can't reinstate your ticket after it is cancelled, and because you are at an outstation (WAW), there may not be a ticket counter that may rebook you properly. To get your money back, I am afraid you have to submit a complaint on AF's website, along with the receipt and clearly state your intention to reimburse the difference of your 2nd ticket (because I suppose that your 1st ticket was cancelled and reimbursed).

PS: only purchase WIFI when you find it needed on board