Walmart.com fraudalent charges on card , Internet

I made a purchase on walmart.com received my item. One week later i received an email saying thank you for your piurchase i opened the email and saw it was another purchase that i never made totalling two consecutive purchases, i contacted walmart immediately, one order was cancelled by walmart but the other was allowed to go through. customer service told me that the order was still processing so they would stop the order. a few days later i was charged for the purchases. i contacted walmart again they told me to dispute the charges with my bank. my bank gave me a reversal for the charges. two months later i get charged again. i called my bank and they told me walmart is disputing the charges stating that they are obligated to take the money and that i did make the purchases. i dont understand how they can steal from their customers.