I've only sent the IRS that notice a few days ago, so I'll have to wait what response, if any I get from them. In any case, I'll be sending a copy of that notice to any taxman who thinks I'm liable, as a proof of my NON-voluntary use of their SSN benefit. Here's what I've sent them:
"My use of the Social Security number, as well as other United States benefits, such as the Federal Reserve Notes, is only under duress and under protest. I wish to cancel that Social Security number, but the ssa.gov website clearly states that it cannot be cancelled, which makes it impossible for me to do so. Therefore I only use it under duress and under protest. And I hope you realize that without an agreement, such as a voluntary use of a benefit, there can be no liability."