Subtotaling of calculated fields in pivot table does not work

I am having issue with subtotaling few calculated fields in pivot table. We generate report from ERP system that provides following items in Excel:
"      Customer Name
"      Invoice Number
"      Invoice Date(when the invoice was created)
"      Sales Order Number
"      Aging Date ( date when the report is exported to Excel)
"      Invoice Amount (fnamount)
"      Days Late ( Aging date  invoice date)
My report attempts to find invoices amounts that are due between 0 days to 30 days past, 31 days to 60 days, 61 days to 90 days and 90 days and above. I use if formula to properly categorize my due payments into correct column.
Here is the example of my If formula:
0 to 30 = =IF('Days Late'<31,fnamount,0)
31 to 60=IF(AND('Days Late'>30,'Days Late'<61),fnamount,0)
In my pivot table I have customer name and invoice number in row labels and all the different date categorize in value. The issue is that subtotal of these different categorize do not provide total.
For example my pivot table looks something like this:
Name                  Invoice #        0 to 30            31 to 60               61 to 90              90 above
ABC CUSTOMER       123456            $1234.00
                          123457                               $1234.00      
                          165468            $100.00            
                          165465                                                    $45648
ABC Customer Total                   $0.00            $0.00            $0.00            $0.00
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