Can I drink sugar free drinks despite my parents saying they will curse me if i drink anything but water.

I am a healthy 21 year old male who works full time as a tradie and studies full time. I am not lazy or have health conditions.

I have given up many things for islam so I don't understand where the freedom lies in this religion when you are a decision away from being cursed at all times

It’s better not to, but if you really want to, then it’s permissible as long as they don’t find out. Do not drink in their presence because that would hurt them, and hurting them is not allowed. If they don’t find out, their curse won’t affect you in Insha’Allah