It is true that the door slam trick is only a temporary fix. It's good when you have your mates in the back complaining that you have a **** car cos your windows don't roll down, just tell them when the car is STOPPED to open and slam the door and the windows work again

If the issue persists, you will need to open the door by removing the door trim and WD-40 or lubricate the bolt that the motor turns to open/close the windows. I don't know too much about this, as I have never opened my doors up like this.

Maybe with my continuous slamming some crap on the bolt had lodged loose and now I can open/close my windows without difficulty.