There are indeed fares that are non refundable and non changeable

There is no policy to refer to, it is simply the conditions that apply to some tickets - some are changeable, some changeable for a fee and some that are not changeable at all

If you have purchased such a ticket, then there is not much that you can do other than claim off of any travel insurance that you may have

What is the route, dates of travel and date the ticket was purchased?