Sales Bar Charts - Are they accurate

The sales reporting funcitonality on iTUnes Connect is terrible. Just a simple barchart that shows cumulative sales. However My Sales Bar Chart keeps returning to zero. I am selling a book through the store, and sales are made and the bars go up by a couple of units but then they return to zero. I have arranged trial purchases of my book to check it is technically working and also to see if the sales will remain accounted for (as I can't be sure the sales dropped to zero because of book returns). However even the sales of my book where I have purchased them and no for sure they haven't been returned disappear off the sales bar chart. I would be interested to know anyone elses experience or get a contact number for iTunes regarding this. I contact them via the website, and received an automated reply promising a response in 2 days but have not heard anything from them