Saying no is considered a wrong response to the general public and that's because people want to use you more and themselves less.
Don't give in to that victim mindset; find your voice and make sure your NO is clearly received.
Don't give people the option to toss you around as if you are nothing.
If you find it hard to say NO, then close your eyes and shout it.
Saying yes all the time doesn't help your personal growth.