St Courier — Items stolen from packet

I recently ordered for masks from a vendor. They had sent 50 counts and confirned me the same before despatch. When i received today and opened there was only 37 abd rest has been stolen. This is the third time i am experiencing this. Previously also similar thing happened and i just ignored. But price of this mask are high abd i had paid for 50 counts already. I am really disappointed with this kind of activity. We are losing trust on your service and i doubr to further continue with your courier.