What 4 installments? Did you send in the 4 1040ES slips? 1040ES are prepayments for NEXT year 2021 return, not your current 2020 Tax Due. Or did they change your return so you owe more?
"accepted" only means the IRS got it and an initial check found no reason to reject it. that does not mean the IRS accepted it as correct. if it finds errors or omissions it will change it and bill you for any taxes owed.
since we can't see your return or the notice, which should explain the changes the IRS made, you may want assistance. don't ignore it. your problems will just increase.
The Audit Defense service is provided by TaxResources, Inc., also called TaxAudit.com, in partnership with TurboTax. If you paid for Audit Defense and you received an IRS notice, call TaxResources, Inc. at 877-829-9695, or report your IRS notice on their website at http://intuit.taxaudit.com/. Do not contact the IRS until you have spoken to TaxResources. They may contact the IRS on your behalf.