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

I'm sending this complaint because Discover Bank did not resolve a fraud claim in my favor. The claim was for 14 unauthorized transactions that occurred between XX/XX/XXXX and XX/XX/XXXX totaling {$1900.00}. I discovered my Discover credit card missing on XXXX, which is the day I called Discover Bank Customer Protection Services to close the account, and file a claim for the unauthorized transactions. I told the Customer Service rep. that I lost the card sometime around XX/XX/XXXX at the time the fraudulent transactions began. I stated that I saw an email about a transaction made at XXXX for {$39.00}, which I didn't authorize, and that led to the realization that my credit card was lost. Furthermore, I answered that I didn't know how I lost the credit card, and that nothing else was lost. I also answered that I didn't have any information on who may have used the credit card.

Next, I received written correspondence from Customer Protection Services that the transactions in question would be provisionally credited back to my account, and on XX/XX/XXXX I did receive the provisional credits. Then, on XX/XX/XXXX I received a voicemail from Customer Protection Services to return the call. When I called, I was asked a few questions from an investigator on the Investigation Team. I was asked if I received emailed fraud alerts at the beginning of XXXX. I answered that the alerts were sent to an email that is used sparingly. Discover Bank didn't have my newer email address that I use on a daily basis. I said I saw the fraud alert concerning the XXXX transaction on the old email address on XX/XX/XXXX, and that is when I discovered my credit card missing. In the same conversation, I was asked if I remember when and how I lost the credit card, and I said what I said on XX/XX/XXXX that I don't know how I lost the credit card, but that the card was lost from my wallet on or around XX/XX/XXXX. 
After this conversation, I received a letter dated XX/XX/XXXX, which stated that the investigation into the account inquiry had been completed, and upon reviewing the facts of the case it was determined that no fraud had occurred on the account. Accordingly, I would be responsible for the entire balance on the account ( see enclosed letter ). 
Discover Bank called me on XX/XX/XXXX, and that is when I learned the claim hadn't been resolved in my favor. I asked for an explanation of why the claim was denied. The investigator asked not only had I received email alerts, but had I also received text message alerts on my mobile at the time the fraudulent transactions were occurring. I stated that I hadn't received any text message alerts, and repeated that the emails were sent to an email address that is rarely used. However, later the same day I asked my son if he had received any text alerts from Discover Bank in XXXX or XX/XX/XXXX, as he was using my mobile temporarily at the end of XXXX and beginning of XX/XX/XXXX while waiting to receive a new mobile phone of his own. My son said he thought he remembered receiving an email from Discover, but that he had ignored it, and then failed to inform me later about the text message. I called Discover Bank back to explain why I hadn't seen the text alert. Hence, I was told by an investigator that the claim would be reopened for a second review, and that I would receive written correspondence within 30 days. Nevertheless, I received a letter dated XX/XX/XXXX ( enclosed ), that said, " based on Discover Bank 's records, the dispute was previously investigated and resolved, and therefore, we are unable to reinitiate the investigation. '' The letter goes on to say that additional information is needed, but I've provided all the information I have.