Train ticket refund

I have purchased two high speed train tickets at one of your agents, CTS for March 26. Due to unexpected schedule, I need to return the tickets. The CTS agent said she did not how to process the refund and said it could not be return. I paid HK$120 fee per ticket and the agent could not help at all. She told me to read the back of the ticket, can I return the ticket at any station in China?