One does not have a cancellation charge for ending a previous arrangement that was never going to be forever anyway. The very suggestion is astounding. Consider, I pay for a TV licence every year; if I get rid of the TV and not watch it any more and so no longer pay to be a member of the TV watching group I don't expect to pay a massive bill to the licensing authority.
What we voted for was to leave the EU not negotiate how much they can screw us for to exercise our right to no longer be a member of the trade block. Plus we didn't vote for a pretend leave only, leaving on paper, and this so called "transition period" is clearly an attempt to find a chance to stay in, in all but name.
It seems that May is failing to listen to her better advisers/cabinet members; and may possibly leave a situation that will have to be revisited when someone, who seems to have more integrity with the principle of leaving, is in charge.