I am a huge fan of DDs. If you show them your receipt and talk w/ the manager explaining the problem you discovered, I am certain that they will do their very best to help you. They are really very reasonable and understanding.
As long as you have this receipt that should honor your exchange
Since each location has varying levels of service, I'd suggest calling to speak with a manager (during off-peak hours) first, let them know the problem and that you have your receipt, and ask when can you come in to exchange the cup. When you get there, ask for THAT manage, identify yourself, and the call. If that manager isn't available, ask whoever is in charge to exchange it and mention that you spoke with [name of manager] who already approved the exchange.
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