excel with a lot of data - how to solve it

I have 2 Excel tables, each with 5 sheets (split by branches). One table is a specification of invoices and the other is a specification of credit notes. Each is filled with up to 500 rows and 10 columns, but I only need 6 of them. I receive these two tables new every month.

These Excel files are specifications of purchased items or returned items.

In column B there is the branch name, in column C the item name, G is gender, H is the Intrastat country, J is the total price of the items, and K is the quantity.

The problem is that this company is not registered for the return of goods.

Currently, I have one large Excel file with around 19 sheets:

•5 invoices

•5 pivot tables created from those invoices

•5 credit notes

•1 instructions sheet

•1 codes sheet

•Retail: items summed by codes and branches

•Customs: here the items are split by customs tariffs

How the file works:

•Invoice sheets: for the pivot tables to work correctly, I first divide the total item amount to get the unit price (J/K). Then I add two columns with this formula: =INDEX(Šifre!A:A;MATCH(C2&H2&I2;Šifre!B:B&Šifre!E:E&Šifre!I:I;0)) this returns the item code. Then I copy everything and paste it as values (because of the large amount of data, otherwise Excel starts crashing).

•Credit note sheets: the procedure is the same as for invoices.

•Then I retrieve all this data to the “Retail” sheet using the formula: =SUMIF(MMB-R'$M:$M$E6'MB-R'!$J:$J)

•Customs sheet: approximately the same formula as above, but here I do not sum by branches, but by tariffs. Here everything is summed together by minus and plus: =IF(SUMIFS('na drobno'!N:N;'na drobno'!B:B;Y8;'na drobno'!C:C;X8)=0;"";SUMIFS('na drobno'!N:N;'na drobno'!B:B;Y8;'na drobno'!C:C;X8)) Next to that, I have a separate table that outputs only the negative amount in case plus and minus result in a negative value: =IF(OR(AA8<0;AB8<0;AC8<0);IF(SUMIFS('na drobno'!L:L;'na drobno'!B:B;Y8;'na drobno'!C:C;X8)=0;"";SUMIFS('na drobno'!L:L;'na drobno'!B:B;Y8;'na drobno'!C:C;X8));""). And finally, in the case where plus and minus result in a negative value, I display only the positive amount; otherwise, I display the combined plus and minus result: - IF(AND(AA9>0;AB9>0;AC9>0);IF(SUMIFS('na drobno'!P:P;'na drobno'!B:B;Y9;'na drobno'!C:C;X9)=0;"";SUMIFS('na drobno'!P:P;'na drobno'!B:B;Y9;'na drobno'!C:C;X9));IF(SUMIFS('na drobno'!H:H;'na drobno'!B:B;Y9;'na drobno'!C:C;X9)=0;"";SUMIFS('na drobno'!H:H;'na drobno'!B:B;Y9;'na drobno'!C:C;X9))).

I hope I explained it as clearly as possible.

Now the question is whether this can be done in a simpler way — something as straightforward as possible and that causes Excel to crash as little as possible.