Can’t say I’ve had much success with visual/kinesthetic ways of letting go. To me it sounds a bit like finding a modern scapegoat. The key chain, paper, and balloon didn’t do anything, why should they receive the brunt of our anger and frustration.
Writing is a good outlet to get emotions out, but I don’t think you need to burn the paper in any ritualistic fashion. Just getting them out there, recognizing that they’re there, becoming aware is a good first step.
Meditation works best and connecting with your values and principles. Although you may have been hurt and are angry, you know truly deep down inside at the core of your being you want others to experience love and happiness and wish them well despite any trespasses they’ve made against you. With that acknowledgement comes letting go and the inner peace that you seek.