Help needed with COUNTIF in DAX

All

Problem: 

I need to allocate the discount to invoice line items, but there are cases when the discount is credited in separate credit memo and has only one invoice line as a result. Then I need to make sure that those lines will be summarized in my column called "AdjustedAmountInvoiceLineItem" using countif function. I tried several DAX commands like COUNT, COUNTA, COUNTROWS in combination with FILTER, ALL, ALLEXCEPT to no avail so far. 

Right now, the value in the last column is zero, but should be -660 EUR.

So this is my current DAX Command:

AdjustedAmountInvoiceLineItem = IF(AND(Table1[Discount]="Discount", Calculate(COUNT,ALLEXCEPT(Table1, Table1[invoiceNumber], Table1[serviceMonth])>1)),0,Table1[Sum of Total]+Table1[AllocatedDiscountPerInvoiceLine])

But I get this error message:

The syntax for ',' is incorrect. (DAX(IF(AND(Table1[Discount]="Discount",Calculate(COUNT,ALLEXCEPT(Table1[invoiceNumber], Table1[serviceMonth])>1)),0,Table1[Sum of Total]+Table1[AllocatedDiscountPerInvoiceLine]))).

I cannot see the error and I am not sure if this is the correct DAX command at all. 

I appreciate all the help!

Thanks!

GracieLee