Immediately call the lender and report the fraud, and stop all future charges.
(Alternatively, maybe the lender reported someone else's perfectly fine account on your credit report by mistake and it happens to be the same one you recently opened.)
By law, if you inform the lender in 60 days of the fraudulent charges, they can make up responsible for up to $50. You can be held responsible for older charges. However, many lenders will not hold you responsible for any false charges if you can prove it. You will have to work with the lender's security department to figure out how this happened that you weren't getting bills or emails. (Potentially someone logged on to your account and changed your address and email address?)
Then I would check all your other online accounts. Change all your passwords (yes, this sucks and will take forever). Don't re-use passwords. You can get a secure app to keep track of multiple passwords if you prefer.
If the lender gives you problems about removing the charges from your credit report, there are other steps you can take later. But most lenders will work with you to cancel the account, block the fraud, and reverse the damage, if you can prove it wasn't you making the charges.
