You sent Bitcoin Cash to your seller and it went through, the coins is in his wallet already. You sent Bitcoin cash so blockchain.info won't show your transaction because it is for "Bitcoin". Bitcoin and Bitcoin Cash are different.
You can check his BCH address here:
https://blockchair.com/bitcoin-cash/address/qp3a5z8ejnc78kzsjuhax4lr2zps75hjqv93ez3amjIt clearly shows 2 transactions, 0.00873000BCH and 0.06100000BCH so if your seller insist he didn't recieved anything from you, you probably got scammed