If you have a problem with getting interrupted, I love starting from the start of the sentence again and repeating everything slightly slower. If they're really bad, then say 'can I finish my sentence please?' and keep going back to the start of your sentence. Once they realise that no matter how much they talk you'll just keep going back to the start of the sentence that they're interrupting, then they'll listen to you, though it might take a while for the message to get through.
If you've been bending over backwards for years, expect people to ignore you when you confront them. Don't be dissuaded, just keep at it. Having a partner to back you up helps loads- when I was just learning how to confront people in a healthy manner, I asked someone to 'go away for a couple of minutes'. They completely ignored me, at which point my OH leaned over and said "look, go away, we'll talk to you when we're ready to", at which point she scarpered :) She now listens to me most the time when I confront her.
Also, expect things to get worse before they get better. People who have manipulated you to bend over backwards for them won't let that control go without a fight. It is DEFINITELY worth it though!
Confrontation is NOT shouting and screaming. It is looking people in the eye and saying no, not giving excuses and not changing your mind and not accepting them talk over you.