The issue is in the data - You have 3 orders but each order is linked to 2 different customers -
Are you trying to say that there are 2 separate order one for customer A and a separate order for customer B each for 10 units - (note that is the result that you are getting in your viz)
Or are you saying that the 2 customers are somehow linked (maybe a bill to customer with 2 separate ship to locations) and the total order is for 10 units?
In the first case you have a one to many relationship linked by the order number.
If your business issue is the second case you need to establish a one-to-one relationship in the data e.g. Order 1 linked to "Customer A/B", Order 2 linked to "Customer C/D"
Does that help?