Sorry for late reply. Please make sure if you’ve been uploading the right file extension.
This happens because by default WordPress only allows users to upload certain file extension (https://codex.wordpress.org/Uploading_Files#About_Uploading_Files_on_Dashboard).
In this case, you will need to do some changes in there. Please try to add this code below into wp-config.php :
You can remove that code after you’ve done with uploading your font. Let us know if you have further question.