Help with family problems please.?

My mum and dad split when I was 3. I'm now 15 and my dad lives 60miles away. He has been married to my stepmum for around 7 years, and in those 7 years I have not got on with her. My sister, 17. is the obvious favourite of my stepmum which bothers me. It just stops me seeing my dad. I usually see him twice a year because he says we should go up to see him and he says it's a long way to drive. My stepmother doesn't get on with my mum at all, as my stepmum has called me a few nasty names, but then denied.Me and my sister usually get upset whilst trying to talk to dad, and he's always in denial. I don't know what to do. Everytime we try and speak to him, it's impossible. Sorry for length. Thankyou.