Hello, Juan!
First of all you should make sure to create WooCommerce Checkout page with [woocommerce_checkout] shortcode in it and select that page next to the corresponding option under WooCommerce ->Settings ->Advanced tab.
Once it is done everything should work smoothly. If the issue persists, submit a request to our Help Desk providing a temporary access to your WordPress dashboard, so we take a closer look at the issue.
Regards,
Andre