I think my parents are robbing me
Why do you think they're robbing you?
By how they are every day, they are cheap thieves
Your first instinct shouldn't be to think your parent's are thieves. Investigate and confirm your suspicions before making any accusations. If you're wrong, you could damage your relationship with them.
I know for a fact that they are robbing me.
If you have a specific event where you can pinpoint them doing this than confront them.  If they know that this is not acceptable, they are less likely to do it.