There’s this quite popular technique, called affirmations. Basically you sit(in front of the mirror if you want), and repeat to yourself in your head or out loud for 5-10 minutes, I am rich, I am confident, I am charismatic, I am good mannered, I have unlimited energy, etc; whatever you want to change about yourself. Now it doesn’t matter what you are or what you think, once you repeat the affirmation for enough time, your subconscious will start to believe it. This is a scientifically proven technique.
If you think about it, if you’re being put down and berated all the time, it’s like negative/reverse affirmations. And it doesn’t matter how strong willed you are, if that’s all you hear, your subconscious will align to that and you actually start thinking you are those things.
Being constantly put down drove me into a dark hole. It made me motivated as well, but it was the wrong kind of motivation. Once you use negative motivation enough, you start to believe that positive motivation doesn’t exist or it doesn’t work, which isn’t true. Few great things were accomplished with negative motivation. It’s always better to use positive motivation.
Two things you should do when you’re in that situation. Remove yourself from the person who’s abusing you as soon as you can. Secondly cultivate self-love. You have to undo all the stuff that was done to you, remove all the negative baggage you’re carrying. There are techniques like guided meditations and contemplation or even the affirmations that I mentioned earlier.
If you’ve been talked to like that for a long time, you start to do it to yourself in your head as well. The people putting you down, they have usually been treated the same way. It’s low self-esteem, they need to put others down constantly to feel worthy of anything. A great book about self-esteem is The Six Pillars of Self-Esteem. People with high self-esteem rarely resort to things like that.
Good luck!