After taking all reasonable steps both legally & professionally, if you don't get paid , move on.
In the grand scheme of things £43 isn't a lot and people like that will reap what they sow in the long run.
Don't let yourself be drawn into pursuing a course that leaves you as morally deficient as they are.
We've all been let down by customers at times, its just a part of life in this old world. Hey ho.