Albert Smith-McDonalds-1699713191

On November 10 I attempted to purchase a medium cup of coffee using my McDonald's app at the Bloomfield CT restaurant on Cottage Grove. I received a code a told the clerk on the speaker. She told me to proceed to window 1. When I got there the clerk told me that my payment did not go through and they could not explain why. I was referred to a supervisor who told me I had to pay because the payment did not go through and she didn’t know why. I asked if I would be billed twice if I paid again. I was assured that I would not be billed twice. I used one card for my mcDonalds app, and paid with another card. Both are American Express. To day I see that I was charged twice for the same cup of coffee and at different prices. I need a refund of the higher amount. What do I need to do?