iThemes Exchange – Limit order quantities to 1

I tried setting the maximum quantity to 1 in the product page and tried switching off the ability to update quantity, but all this does is stops the user from being able to change the order quantity. My site is randomly sending multiple orders on checkout as I’m testing out the payment system. Its a subscription service I’m running, its only supposed to place 1 order at a time. How can I prevent exchange from adding multiple orders to the cart?