CP 13 notices indicate the IRS made changes to your return because they believe there's a miscalculation on the return. You're not due a refund nor does the IRS owe an additional amount because of the changes. Your account balance is zero.
This is generally done when you claim a refundable credit you do not qualify for or claim a payment that was not made.
Review the notice for an explanation of what the IRS changed and why.