We use an automated security tool to verify key pieces of information such as billing and shipping addresses. If the tool cannot verify any or all of your information, the order is canceled automatically. This might be the issue that you are running into. To ensure processing it is best to keep the billing and shipping address the same whenever possible.
We recommend to place a new order via PayPal using their buyer and address verification system to make it easier for your next order to process. Or if you have recently moved we would recommend updating your billing address on your payment card and replacing your order.
Alternatively, one of our resellers might have the parts you need and may be able to process an order for you. This page will give you a list of some of the other places where you can purchase Crucial products: