Paxful isn't at fault from what I see.
As stated by tonguetides:
Did you provide proofs as well? Paxful aren't idiots and if you provide screenshots for "example: live chat with support service asking when the coupon was used" I'm sure they would have been glad to intervene in the dispute.
You shouldn't panic like your staring at a gunpoint.
You're in front of a PC FFS, make use of your resources and report the baddies.