Shamed is what one does to you.
Ashamed is about how you feel about yourself.
Shamed could be punitive, ashamed shows remorse sometimes repentance.
If a person has no shame, then others might view their behavior or conduct as shameful and thus shame them, but the individual who has no shame is not (yet) ashamed of anything they have done or are doing.
Below is paraphrased from Webster's fourth edition
To shame is to dishonor, or disrespect
Shamed is when others treat with dishonor and disrespect due to some action or trait of the one being shamed.
Ashamed is when you are embarrassed by these same traits - or when you fear shame/dishonor/loss of respect even before said actions are publicly known