To me it would depend on what you did that they resorted to taking away your car and if they own the car. Sorry, but even if you turn 18 - if they own the car, they can refuse you use of it. ( If they own it, it would not matter if you just turned 70, they could 'take it way' if they chose.
Also, the silent treatment is a pretty harsh way to deal with issues, unless they are outright abusive. Especially if you are living in their home. Keeping the bridges of communication open would the way to go, IMHO. There is no polite way to tell anyone that unless they give X you will no longer talk to them.
In order to earn back the use of the car, you need to prove they can trust you again, and then maintain that trust.