There really is no easy way to open the door when it is jammed like it is with the belt in the latch.
The only way is to have one person on the outside pulling on the door handle and the belt and have another person inside the vehicle and pulling the inside release handle and pushing with their shoulder on the door. This should release the latch and open the door.
Be careful with the inside door release handle, if you pull too hard, it will break. It is only plastic.