Icons breaking in modules

Hi,

I’m trying to add the email icon via the shortcode (✉) into the content of an icon box. I find that although the first time the icon appears as it should, if I update the page and do a hard refresh the icon becomes a question mark. For example in the top left icon box on the below page I’ve tried to put an icon near the email address and it has broken.

Is there a specific instruction I’m missing? If possible, I’d also like the icon I insert to have the circle around it for more definition.

Thanks!