My iMac it's not updating to the latest MacOS

Hello, I have a late 2012 iMac and it has installed MacOS High Sierra (10.13) and I've been trying to updated to he latest 10.13.3 but it's not doing it, I download the update, I click on "Install" and the computer reboots it self and does all the thing it normally does when an OS update gets installed. But when it finally finishes, when I click on the Apple logo on the top bar and then I click on "About this Mac" it says that the current version of the OS is 10.13 and then on the Mac App Store shows that I have the same update I just installed available.

My question is why is the system not updating and how can I fix it?

Thank you and best regards