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.
