Problem with a purchase shown on your statement: Credit card

I received an email from Bank of America that they are sending me a replacement card due to the future expiration of my current card. I never received the replacement card that was issued for my account. Before discovering the fraudulent charges, I contacted the bank and informed your representative that the replacement card had not been received. During that call, I specifically asked whether the card had been used and was told that it had not. I also requested that the card be canceled and replaced. Despite this, fraudulent charges totaling more than $4000.00 later appeared on my account. I did not authorize these transactions, did not possess the replacement card, and did not benefit from these purchases. I called the bank, and they started an investigation and issued me a temporary credit. In less than 24 hours, I received an email from the bank stating that they had completed the investigation and found me liable for $4000.00 in fraudulent charges, and they removed the credit. Since then, I have called the bank a few times to reopen the investigation and have requested complete information regarding this claim, which the bank has never provided. They keep telling me the investigation is still open, but at this time, I am liable for these charges, and it's been a month since I filed the initial complaint.