Trainline Outrageous Change Fee For Last-Minute London-Edinburgh Trip

I tried to reschedule my London to Edinburgh (Waverley) journey, which I reserved about a month ago, for a date four days ahead. Since I couldn't do it through their website, I called customer service. After listening to me, the customer representative said I had to pay a fee for this change. There are still four days until the departure date, and the fee they ask for is more than half the ticket price. I wanted to postpone because my girlfriend got sick; we had planned the trip together. As for the option of canceling and getting a refund, they only refund a fifth of the ticket price. They have truly malicious customer service and cancellation policies.