How to link shipping costs with field?

Hi,

I made an extra field for customers so they can choose if a package will be send to a shipping or billing address. In the Netherlands it is free, but abroad is 20 euro. So when someone from abroad orders a package it will be 20 euro but hen billing address is abroad the same. You get the idea I hope.

However, it puts 20 euro there, no matter what and it should be free in this case.
How can I do this? Do I add a special key to this field? Or can I use a snippet?
https://prntscr.com/kdhvnk (choice to send the package to billing or shipping address)
https://prntscr.com/kdhw1j (costs are not correct here)

The page I need help with: [log in to see the link]