How to get a refund for GCN subscription?

This is related to this discussion, with the same situation: Subscription provider rebate for terminat… - Apple Community

Has anyone successfully requested refund for a terminated subscription? GCN support has said that I have to request a refund through Apple. I tried through the usual channel, but GCN does not appear in the list of apps whenever I request for a refund. Please help me with a step by step guide. Thank you very much.