I'm having a problem with lag in the game.

Hi, I have a problem with the game.
I need help and advice on what to do.

The thing is, when I enter the game, it lags a lot.
I thought it was my internet connection, so I connected to a different internet connection and the same thing happens.
I watch movies and everything works fine, except for Diablo lag.
I've messaged people on the game, but no one else is experiencing lag.
Please help.