Originally Posted by Dave Noble

Assuming it was a PC code that you otained legitimately and should have no reason not to use it, then no reason not to open a dispute with a credit card company

If it was some code found trawling the internet for codes , then quite reasonable for the company to not honour it - some codes have required certificates to be surrendered at time of rental and are only valid for 1 use with that certificate

I cannot imagine any chance of ending up on a DNR list for a valid dispute