Does this happen even if you first return / quit to the main menu, disable the addon and then load the map again?
If you wish to disable the addon while playing without quitting to the main menu, you'll need to run "mat_reloadallmaterials" in the console (no other way around it I'm afraid), but, in my experience, that can be a bit buggy with regards to lightmaps...

I disabled the addon and reloaded the map and it still remained the same.

If you are absolutely certain that the addon is disabled and the issue still persists after restarting the game, I think the next step is probably to try and unsubscribe + run "menu_cleanupgmas" from the console (to delete unused addon files) as it sounds like G-Mod might be acting up on you...

If that is still not enough, I personally would manually delete the "GarrysMod/garrysmod/addons" folder or go for a full clean re-install.

I'll try that, and then I'll tell you

It works now, gmod was being weird, but it's working properly. The addon stops working after disabling as it should