Contact Amex to close the one you don’t want. “Activation” is just a card security procedure; the account is open until your close it.

There is no point in contacting the credit companies; they will first want to know if it is identity theft, which it is not. Given that it’s not identity theft and the card is open in your name, they cannot remove it from your report; the card must be closed through American Express. Although you did not do the confirmation process to fully activate the account, the account is still open, and only you/American Express can close the account. Although it is an error, it is not an error in the reporting by the credit bureaus. Make sure that when you contact American Express to close the card you clearly state that you want the account fully closed and you do NOT want any sort of replacement card. They may require you send them something in writing (via mail or fax) to close the card; if you do send them something, again, make sure to clearly state you want the account fully closed as it never should have been opened in the first place.