Shipping method to be hid after an amount

In a wordpress/woocommerce platform, I have set free shipping for all orders over 15 euro. For orders under 15 euro, I have set a fixed shipping cost. Problem: When the customer adds in the cart products over 15 euro both of the above shipping choices are available. That causes many times customer misunderstanding and me running for shipping cost refunds all the time.
I need only the option of free shipping to be available for carts over 15 euro.
*I need that for any amount I want the free shipping to have. For example if I change the amount for free shipping from 15 to 20 euro, I need this option available from 20 euro and the fixed charge option to be deactivated.
** I also have a pick up option from my store. It is shown and available at any cart amount. I need it to remain active as is now.
Requested results:
-> For carts 0-14,99 euro I need a Fixed shipping charge available choice with radio button, Free shipping method to be shown but with a deactivated radio button and Pick up from store as available choice.
-> For carts 15+ euro, I need a Fixed shipping charge to be shown but with a deactivated radio button, Free shipping method to be available choice with radio button and Pick up from store available.

THE BUDGET IS FIXED. PLEASE ONLY PROPOSALS FOR THIS AMOUNT. I NEED THIS TO BE DONE IMMEDIATELY AND I WILL PAY YOU RIGHT AFTER IT IS COMPLETED. ANOTHER PROJECT IS READY TO BE START AFTER THIS ONE IF WE AGREE.