Complaint sub-issue: Credit card company isn't resolving a dispute about a purchase on your statement

On XX/XX/2017 I made a large purchase for 3 XXXX gift cards at XXXX # XXXX. After running my Discover card a computer error occurred and a manager was called to assist ( Transaction # XXXX ). The manager informed me that store policy states a customer can not purchase 3 of the same brand gift cards in one transaction. Due to the computer error no cancellation receipt was printed. I then inquired if I could purchase 3 different brand gift cards in the same transaction and the manager confirmed I could. I then purchased the 3 different cards ( Transaction # XXXX ). I than left the store and called Discover to inform them of the indecent. Discover informed me that I would need to wait a few day for the transactions to process and the cancelled transaction would be credited back to my account. Without digging into to my phone records I do not have dates or the exact amount of calls placed to Discover. Transaction XXXX was in the amount of {$1500.00} and transaction XXXX was in the amount of {$1500.00}. After investigations by Discover I was told XXXX validate both transactions so I requested they open the disputes again. Discover reopened the disputes. The next time I called I was told that the disputes where settled so I requested info on the validation and discovered both transaction where validated using the receipt for transaction XXXX. I informed Discover of this error and reopened the disputes again. lack of communication from Discover caused me to call them to check the status again. I was informed that the disputes where closed and validated. I again requested that the disputes be reopened due to the inability of Discover to properly validate both transaction again informing them that they validated two different transaction with the same receipt. They informed me that the time frame to dispute one of the claims had passed and they can only open one. This turned into a supervisor review of the dispute and more time wasted. The next call lead to Discover informing me that there is nothing they can do and should take my depute to XXXX. I contacted XXXX and they sent me to the store manager at the store the transactions where made. The XXXX manager informed me that they have very little information on transaction as old as this ( Past 6 months ). However the store manager allowed me to photograph a department sales report and void receipt. This was all they had left of the on file. This information showed transaction XXXX voided. I called Discover and gave them this scanned photo. Discover sent it for a second supervisor review. Shortly after I received an email stating " After reviewing the information you provided, we determined that we've already considered this information or it was insufficient and we could not continue the dispute. '' I put my faith in Discover to properly validate these charges. I informed them multiple time of the error in there validation of two different charges with the same receipt. Discover left me n a situation where I have to pay them for a {$1500.00} transaction that was not validated, interest on the amount and drop in my credit score due to the added balance.