I checked I have no order from this guy on FBA or FBM but still asking me to refund money and only charge for whatever the price he is thinking right or else telling me that he will report me for price gauging.
You can send the order number to Amazon to check the order. This happens when the buyer gets confused with seller especially when they have bought more than 1 item from different sellers at the same time.
In terms of price gauging, any negative feedback he leaves will be removed by amazon if you request removal