Parents strange love? How to deal?

My stepmom and dad have perplexed me all my life but now I'm really at a loss. All I ever heard for years was how much they wanted a grandbaby and now at 33 I finally have my first son, their first grandbaby and they are nowhere to be found. My dad works a lot but my stepmom does not work. They live about 45 minutes away from me but come to my city weekly but never visit. I tried calling last week to let them know I was coming to visit but they didn't answer and have never returned my call. My stepmom does not like visitors so I can't just drop by unannounced. I do not feel welcome at my parents home, I even knock when I go there to visit! She's been my step mom for over 28 years. I haven't heard from my parents in over three weeks! Stepmom doesn't like to answer the phone at home even though she doesn't work, doesn't have friends and only goes out to shop. She hasn't called me to see how I'm doing in years. I have to call her and then she usually doesn't answer.