Can Wal-Mart keep my paid merchandise

My wife used self check out and was told that $30 worth of merchandise did not scan so Wal-Mart said she stole the merchandise. We had merchandise from Wal-Mart pickup that was paid for along with almost $70 worth of merchandise that did scan and was paid for. They kept all of my stuff I had picked up and that was paid for. I paid with my bank card but they told me they weren't gonna give it to me and they could charge me with accessory. Can they legally keep my merchandise?