I have totally lost the plot. I should be in a mental institution.
No, they should be in mental institutions. Don't you remember, the first sign that you AREN'T the crazy one is that you wonder if you are!
I don't know how to advise on this unauthorized phone usage. This is really tough love, but maybe you should consider changing your door locks, so S is obliged to spend H's money on phone calls.
As to H's nastiness, maybe remember his is just another teenager having a tantrum, no more or less mature than S. I wouldn't worry about hating him temporarily...remember, the opposite of love is indifference, not hate, FWIW.
I really don't know about the phone business, just wanted to offer support. Maybe your L has an idea?
