Yeah, if this is as you describe it here, the GM action makes no sense, as - again going by your description - this is within accepted game behaviour and use of game mechanics. Heck, it’s even part of EVE University’s wiki. Just like it is explained to New Players in the New Citizens Q&A section.
Now if this were in a starter system, that would be a different case. Likewise if it were to deal with Plex or character sales.
Again, going by what you’ve described (but we have no idea here as to whether that is complete or accurate) CCP’s Reimbursement Policy (Item 8) seems clear.
You’re certain you didn’t do anything fishy? But, in before the lock I suppose. This should be between you and Customer Support.