Absolutely; if you have any documentary evidence that you were promised unlimited refills for life, as opposed to for an indefinite period of time, then definitely push the issue.
From what I have read (don't know if is true but I believe it is) at one time Disney Offered a lifetime pass-- long before refillable mugs-- now if some has them: first can I be your friend second this is an issue worth pushing over a $2 cup of soda that you need to go back to your resort and then the food court to get....