Help! Opencart 2.0.3.1 not subtracts the stock

Hi.

I have optimized Opercart time with several modules and when I have everything almost done I realized that when the process is done through the web, the stock is not discounted and this is a problem for me.
Can somebody help me? I searched the marketplace to see if there is a module that solves this problem but I have not found anything ...

Thank you very much in advance.

Regards.