Product: Credit card

on XX/XX/year> I received a Chase fraud text.. An attempt to charge {$8400.00} on my card was made and declined. I called the number on my card and made clear that it wasn't me. My card was cancelled. During the conversation it was discovered that another charge in the amount {$4500.00} was successfully charged earlier that morning. I made clear that I didn't make that charge either. That charge was to XXXX and XXXX XXXX was the seller. The item purchased was a laptop computer and it was sent to my house. 
A XXXX search as to why a cyber criminal would use my cc information to send merchandise to me reveled a scam where the criminal has taken over your account on a website. When you attempt to return the fraudulently purchased merchandise through the website, you inadvertently wind up sending it to the scammers. In an effort to prevent this from happening on XX/XX/year> I called the number on my card and asked to be transferred to a fraud specialist. I explained the situation to the " fraud specialist '' and was instructed to hold onto the merchandise and that someone would get back to me to help me safely return the merchandise. Nobody got back to me and two months later the charge was back on my account with an explanation that I was responsible because, " the merchandise was either billed to my address or shipped to my address ''. 
The next day a went to my local Chase bank and got help from a banker. He took my story and documents I provided and escalated this through customer service. They called me and recorded my story and several weeks later called me and told me to contact Chase Fraud. I contacted Chase fraud who told me I needed to provide something from XXXX showing a fraud occurred. I provided them with the only document I got from XXXX which said that there was a new sign on from a new machine on my account. That was on XX/XX/year> after I returned home and signed onto XXXX from the only computer I ever use for XXXX. I signed on to try and stop the transaction and to change my password. A few weeks later Chase fraud contacted me by phone and told me that I had replied to an email from them regarding the {$8400.00}, saying that it was in fact me trying to make that purchase. I never received that email, nor responded and can't find any sign of it on my computer. That afternoon I got a letter from Chase fraud saying I am responsible for the {$4500.00} because it was a " valid transaction '' At this point, it's clear that Chase is not helping, and I decide to try and physically return the unopened merchandise to a local XXXX XXXX store. I was sent home and had to get approval from XXXX XXXX support. Ultimately on XX/XX/year> I returned the unopened package and was given a receipt for {$4500.00}, which I believe it the total amount less the XXXX charge. The receipt was to put the money back on my cc account through XXXX. The refund did not get back to my account. With help from a banker at my local Chase branch and most of all help from XXXX XXXX, I received a check todaXXXX XXXX 
My understanding is that I am not responsible for fraudulent charges on my credit card. How is it that Chase bank has the legal authority to just declare that no fraud occurred, and dump this mess on me. This has been over six months with nothing remotely helpful from Chase credit card services