A really good letter Cofty. I think your hurt at their cavalier attitude towards you comes through strongly without being judgemental towards them and your puzzlement at the way they have shown no concern towards you in recent months despite your battle with your illness. It shows clearly the heartlessness of this doctrine that they can put aside the normal unconditional love a parent has for their child (no matter how old). I hope it affects the way they are towards you in a positive way.
I can't see how they could fail to be moved by it.