Keep the law about time for resolution of billing errors in mind. The card company only has 90 days max (actually a little less without getting into the somewhat complex rules) to RESOLVE the problem. If it is not resolved within that time they should drop the charge permanently.
I won several chargebacks, including one large car rental in Europe.
For some reason, the card companies find it very difficult to meet the deadline. I suspect a lot of them don't even know about the rule.