Please ensure that the second transaction is not a refund/return being assessed to the account. If it has a positive reflection on your balance, it could be a return of funds.
It is also possible that an online purchase was itemized into smaller individual charges due to the way the shipping centers operate (for example, Target.com is known to do this). Try at the surrounding transactions to see if they total up to the full order amount.
If you believe you received a duplicate charge on your account, please contact our Member Services Team at (833) 264–6447 or email@example.com.