Problems signing up for prepaid internet, and now i need a refund because of duplicate charges

Several days ago, I was at an xfinity retail store inquiring about prepaid internet services. The associate who was helping me needed my payment information in order to continue with the transaction and create my account. So he swiped my card to finalize the transaction and the computer read "error", then prompted him to start again. So he tried again, and another "error" message. No receipt was printed either time so no need to think I was being charged $83 twice for an error that still left me without my prepaid internet services. So he realized he was using the wrong computer for the transaction, so we moved and we finally were able to finalize the transaction. In the meantime, i realized i had bank alerts stating i was charged now 3 times for one service. Now the problem is when i try to contact someone about a refund, there are no transactions on record for the first 2 times because i didnt have an account. I need help