My family doesn't call on anyone else but me?

Here's the thing, I'm really big on every sibling pulling their weight in the house but my family makes that impossible. I'm 16 going on 17 and my sister is 12.
When we were younger (11 and 6) I could understand when my family would only call me to download stuff on the computer, bring them stuff from their rooms, the kitchen, anywhere in the house. But fast forward 5 years, NOTHING HAS CHANGED. In fact it's gotten worst. Here are some examples.
1. My sister will be in the SAME room as my grandma and I'll be in my room upstairs doing something. My grandma will completely disregard the fact that my sister is at her disposal and call ME to come downstairs to get her some bread, bible, water etc. While my sister lounges around.
2. My mom wanted to download an app on her phone. My sister is right NEXT TO HER but calls me from the basement. Keep in mind my sister has had 2 iPods and an iPad and is capable of downloading viber onto a phone.
3. My aunt is new here. If she needs to find something like mosquito repellent, telephone, or how to log on to the Internet. She'll ALWAYS call me 10 out of 10.
There's plenty more but there's a limit on characters.
It's not like I don't want to do these things. There easy and effortless. My problem is that they will call me even when someone else is there. I have to stop what I'm doing when it's not necessary. It's very frustrating to come up/Down stairs to help with something, just to find your sister on the couch playing w/ iPod unbothered.

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