If you're trying to farm for a card opening packs, then you can do the following:
1. Buy any packs you want, spending all your Duel Points.
2. After you spend all your points, DO NOT leave the card shop or attempt to go into another game mode.
3. Simply press the HOME button on your PS4 controller, highlight Yu-Gi-Oh! Legacy of the Duelist and hit the options button.
4. Choose CLOSE APPLICATION, then restart the game.
5. If done correctly, all your points would be refunded completely.