fix number of items in cart ( need to be done in next 1 or 2 hour's max)

I want to prevent double orders in wordpress WooCommerce. When you go to my shop, you need to buy the item only once. Sometimes customers will buy it twice. I then have to refund them manually. I want to prevent that. The shop is large, so it has to be a global fix

i have more than 600 product ..

bid with "i can fix them in next hour"

$20 budget fixed