I know you may think it's nearly impossible but the possibilities of you being scammed is high D: Perhaps the other person forged the "not paying" part.
You should ask them to take a screen shot of their point balance before they send the payment, then show the balance after as proof that they really DID send the points. Also tell them to screenshot their transaction history as proof that they didn't send to a side account and pretended that it didn't work.
This is for your own safety haha C: If it really /is/ a bug, try contacting the Help Desk! I'm sure you'll figure it out somehow <3