DOT rules require that your baggage allowance be printed on your e-ticket receipt. Presumably that shows the free bags. Send that off with your CC dispute and you should see your credit soon enough.

As an aside, it's always worth having a hard copy of your e-ticket receipt. The agent sees what you see on your receipt and that is what will govern your flight. It's also helpful because if you see an error on your e-ticket receipt, e.g., no free bags, you can get that fixed in advance.