Change happens. It makes sense to get in touch in advance if you know that trip is cancelled or needs changing. Life is busy and sometimes its forgotten.
Worry not. All ticketed items, Flights and Rail, are tracked any unused tickets are automatically refunded subject to the rules of the ticket. Not everything is refundable but if it is, then it will be.
There is not a lot more to add, no action is required, it just happens and is part of the quality control functions and a feature of low touch administration.