I received a CP24 from the IRS, explaining my overpayment of estimated taxes and refunding the difference. But, it doesn't match with the refund expected from my Return?

The IRS changed your return because it found a difference between the amount of estimated tax payments on your tax return and the amount posted to your account. 

what to do if you disagree

https://www.irs.gov/individuals/understanding-your-cp24-notice