Problem in FontAwesome Icon selection in Customizer

Here’s the scenario – I want select to select fontawesome icons from the dropdown list but it’s not working. For some reason the class inside ‘span’ isn’t adding up(I have tried jQeury append,css) but so far no luck. ANY help would be appreciated,
Here’s the screenshot – https://imgur.com/ATtLiUi
Here’s the code – https://pastebin.com/5MD2WscM