I am really sorry about your loss and it's no wonder you are feeling very sad, very angry and just down right pi....d off about cancer.
I know nothing can make any of it feel better but know how important those daily phone calls were to your Dad. In fact sometimes when we live close by we actually have less contact than you had with your Dad. It's normal to feel cheated of one last visit, one last cuddle, but even when it is someone's time to leave us...we don't always know when that will be and feel cheated. My Mum passed peacefully in her sleep...quite unexpectedly really. Although I felt her loss extensively I was pleased in some ways...pleased that she just went to bed and didn't even know it was going to happen, that she didn't need to go into supportive care, and that she had joined my Dad who had passed before her from cancer and she missed terribly. None of that made my loss easier, only that I was pleased for her. I will always miss both my parents. But as time goes on you will remember with loving warmth not just heartache. How long until then is unique to us all.
You are going through a tough time, in the middle of treatment and probably feel quite alone in it. We are here for you as best we can be. I hope you can re-establish some sort of relationship with your sister, I know with mine we have made an effort since my mother has passed and meet up once a month.
Kath x