I received CP60 notice saying I need to pay $1,523(1,518+5.25) but I already paid the $1,518, I have the confirmation and doc. Why am i getting this notice??

How did you pay it, and has it cleared your bank/credit card company?

I paid via bank checking account, and the IRS deducted.

call the irs at the phone number in the notice.   this could be a case where you return was processed before the IRS processed the payment.