Each card network has its own formal, structured process for handling disputes between cardholders and merchants, but at a high level they are all essentially the same. The process is described here:
After you receive a dispute you have one decision to make: will you challenge the dispute or not.
If you choose to challenge it, you will need to provide a response -- your evidence -- to the issuer of the card:
The evidence you provide the issuer at this step of the process is the only communication between you and the issuer. There are no other opportunities to communicate during this process. Based on the evidence you give, the issuer will make a single, final decision about whether the dispute is won or lost.
If you choose not to challenge it, you can either ignore the dispute and do nothing or explicitly accept the dispute: