A CP 13 letter is sent when IRS made changes to your original return because of an error, resulting in a zero balance. What this means is whatever amount of refund, was incorrect, and after the IRS corrected your return, there was zero refund. My guess is because the IRS indicated affects the following area of return. Recovery Rebate Credit, that you said you did not receive the Recovery Rebate Credit and the IRS records show you have received the Recovery Rebate Credit. Check your bank account and see if you received an amount equal to $1,400 per person (if you filed MFJ and no children) this amount would be $2,800. It would have been deposited sometime during February or March 2021.
