Woocommerce Shipping cost display

On my Woowommerce online shop, on the Cart page before proceeding to Checkout, I do have my Cart Totals, this includes shipping cost as well. The shop business rule is that for all orders above $700-00, shipping is free and for all orders below $700-00, we charge a flat fee of $90-00.

Cart with an order of below $700-00 is working perfectly and displaying as expected.

However, my problem is that Cart with total cost above $700-00 its showing two radio buttons, that is, Free shipping and Flat rate. I want only one radio button to show. The button that must show is Free Shipping since order is above $700-00 and it must be marked already.

So, my question is how then do I deactivate the Flat rate radio button so that it does not show on any orders above $700-00.