/* 1. Added !important here to match your top header rule */
#RegisterForm div.scSummaryTotalAmount div.scSummaryTotalQuantity { 
    display: none !important; 
} 

/* 2. Removed "#RegisterForm" from the front of these IDs (explained below) */
#GenericBillMe01 .Row-PaymentStartDate { display: none !important; } 
#GenericBillMe01 .PaymentFrequency { display: none !important; } 
#StarRequiredNote { display: none !important; } 

/* The rest of your working code remains perfectly untouched */
#RegisterForm header.BlockHeader { display: none !important; } 

#RegisterForm #agyInfoFrame, .Area-EventManagement .Classic, .Area-EventManagement .DashBox table, .Area-EventManagement .Leftalign, .Block .IndProfileInclude td, .Classic, .Designations, .EventCalendarDetails .EventCalendarTable td, .Page-IPledgeDes1 .AgencyDesTable, .Page-IPledgeDes1 .PartnerAgencyDesTable, .Page-IPledgeDes1 .WriteInDesTable, .Page-IPledgeDes2 .AgencyDesTable, .Page-IPledgeDes2 .PartnerAgencyDesTable, .Page-IPledgeDes2 .WriteInDesTable, .Page-OProfile .Table-OrgProfile td, .PledgeDes, .PledgeDesD, .PledgeDesH, .PledgeSum, .PledgeSumD, table.CBPackageDtlForAccount td { display: none; } 

#RegisterForm #PledgeTypeSelectionBlock { display:none; } 
#RegisterForm .Section-Survey > div { display: none !important; } 
/*#RegisterForm #GenericBillMe01 .my-3-PaymentMethod { display: none !important; }*/

#RegisterForm div#IndInfoBirth {
    display: none !important;
}

#RegisterForm #IndNameTable > div.col-sm.Col-Input.Col-NamePrefix {
    display: none !important;
}

#RegisterForm #IndNameTable > div.col-sm.Col-Input.Col-NameSuffix {
    display: none !important;
}

#RegisterForm div.col-sm-12.Col-Input.Col-CountryCode {
    display: none !important;
}

body.Body-Page-SPRPThankyou tr.Row-Account,
body.Body-Page-SPRPThankyou tr.Row-PledgeType, 
body.Body-Page-SPRPThankyou tr.Row-BillFrequency, 
body.Body-Page-SPRPThankyou tr.Row-BillStartDate, 
body.Body-Page-SPRPThankyou tr.Row-PaymentMethod,
body.Body-Page-SPRPThankyou tr.Row-TransactionType { 
    display: none !important; 
}