To clarify, the Recovery Rebate Credit was on line 30 of Form 1040 but the total refund you received was less then the amount shown on line 34 (the Recovery Rebate Credit is included in your total refund)?
You might want to check if the IRS adjusted your refund because according to their records they had sent out the stimulus payment. Please see Get My Payment.
You can also check and can call 1-800-304-3107 to find out if you had a FMS offset that affected your tax refund. Please see Treasury Offset Program & Debt Management Services for additional information.