Pop-ups advertisement / lack of wifi connections / virus

Few months ago, I was trying to download a game (old game from random website) that required me to download other abnormal apps. Within an excitement, I instantly downloaded other weird apps without thinking how badly it could damage my laptop. After that, it has made my computer to proceed in a slower pace, lack of wifi connections, and pop-up advertisement keep shows up every minute or so. I have now deleted all the apps, reseted my computer, and downloaded the new update on Apple, but the virus would not go away.

Are there any suggestions what I should do?