You may see "Application for Refund" as the title of a form that you have to fill out. If you are asking for this form by name, you might say:
"Could I please have an Application for Refund form" because that is the name or title of the form.
But when you are asking for a refund you say something like this depending on what the process is for getting the refund:
"I would like a refund, please."
"I would like to apply for a refund, please."
"I would like to fill out an application for a refund, please."
In the last case you are asking for the application form without knowing its title.
Please note, I'm not saying it's a rule that articles are omitted in titles, I'm just saying it seems fairly common in form titles. This may be an example of the world failing to understand and follow the rules of grammar. For example: