Difficulty in customer analysis

I'm finding difficulty in doing a customer analysis with the data presented to me. I have the following data presented in one sheet.

Date, Customer Code, Customer Name, Net Sales, Qty, Profit, Item Name, Item Code,Branch Name , Category , Sub Category, Department

I'm unable to get accurate calculations in PowerBI whilst finding new customers, lost customers, and repeating customers. For eg. The data is for this year and last year, and I have obtained the no.of new customers and put it on a table. However, when I export it to Excel the number of new customers is even more. Would it be better to separate the data into separate tables and import it to Power BI?  

This is how I would define the new, lost, and repeating as I have created a dynamic slicer of (net qty / sales / profit) so I would like to see new/lost/customer by those values 

New Customers - Count Customers who made their first purchase 

Lost Customers - Count Customers not present this year

Repeating Customers - Count Customers present in both years