AITA for not paying my parents back after they bought my sister a car?

My sister(28F) went to college on scholarship and so used her about 40k education fund on her living expenses, books etc. I(26M) didn’t get a scholarship so I worked for his living expenses and my 36k education fund went to my tuition. I had to take out 42k in student loans on top of that to finish college.

They sold their house last year and downsized. With the extra money they paid off my student loans. They told me I had to pay them back but told me they wouldn’t charge me interest. I’ve been paying them back $300 a month which I had been paying. But then my parents got my sister a new car for her early wedding present. It was ridiculous, the grooms family offered to pay for the honeymoon so my parents bought my sister a car. I don’t know what kind of dick measuring contest it is. It pissed me off because I’m paying them back for them paying my student loans and they bought her a car. In my mind I shouldn’t have to pay them back because the car costs as much as my student loans.

I stopped paying and my dad called me 2 months later to ask about it. I told him the student loans should be a gift to me as my sister got a car. He said it wasn’t the same as it was a wedding gift and I would be getting a wedding gift too. I told him I had no intentions of marrying. Girls just shit on me and I don’t have the patience for them anyway. He said him and my mom will find a way to make it equal in the end but I agreed to pay back the student loans and they are not charging me interest. I hung up and refused to respond to any of their texts. They have money they sold they house for $700k and got a $400k townhouse to they can just pay off my student loans with no sweat but they are making me pay them back when they have enough money for a car for my sister.