The free undercoat is only included in the first order. It is designed to introduce you to the product in the hope that you will buy it in future orders.
On you first order it was automatically added to your basket but on the subsequent orders if you are logged in it will not show in your basket.
If you are not logged in it will show up and this can cause confusion. However, it is always shown as stating that it is a first purchase offer when it is placed into your basket. Please see the screen shot below.