What train was this? And what kind of ticket? And why did you miss the train?
Most standard tickets are for a route, not a train. The fact that you start the purchase process by selecting a train does not mean that you are actually buying a train ticket. And with such tickets if you miss a train, you just take the next one. There is no need for a new ticket.
It is difficult to get a refund for a ticket after the fact, as there is nothing that proves that a ticket has not been used. But you may under some circumstances. But we need to know more details. So tell us what kind of ticket you had, where you bought it, and for what train it was.