Hello Anna,
The customer Balance Report can be found under AR/Reports/Status/Customer Balance list.
There is also 2 reports that specifically provide you some Information on customer invoices
(a) AR/Reports/Statistics/Invoice/InvoiceTurnover and
(b) AR/Reports/Statistics/Invoice/Customer Invoice Journal.
You have to find out which Report suits you best.
Personally, I am a fan of the inquiry forms that e.g. Sohaib mentioned as they allow you some Kind of personalization and a very easy and fast way for analyzing your data.
All the best,
Ludwig
P.S. Please let's close the case if you found your answer as already many community members replied. Thanks.