I do have to say that highlights damage hair. It's good you just highlighted instead of doing your whole head. I had some highlights about five years ago that I'm growing out now. (I sort of trim the highlighted parts only, and have about two inches left in my hair before the highlights are gone).

Unfortunately, your hair dresser damaged already damaged hair by flat ironing your processed hair. Lightening our hair can straighten it a bit, so it makes sense that you have all these different textures now. So I hate to say it, but the processed part of your hair is now very damaged. I doubt it will go back to it's "correct" texture until it grows out. If it's driving you nuts, I do think you will have to trim off the damaged parts.

Deep conditioners/conditioners (they are actually the same products, just packaged differently) can help make your hair more manageable, but nothing can repair damage, no matter what promises a product may say. Protein conditioners might helps very slightly, but they never helped my hair back in the day when it was very damaged, unfortunately, and they probably won't make any noticeable difference if you have hair that's really damaged.

The good news is that you didn't do all your hair with highlights, and that hair does grow out. Do try to be as gentle as possible with all your hair, and maybe stay as far away as possible from hair dressers who feel it's okay to hurt your hair like that. If you don't want to cut off the damage, you could always set your hair, like in two strand twists, to hide the different textures until you are ready to trim off the damage.

It really makes me sad a hair dresser would do something like that. I know this isn't great news, but I hope it does help in some way.