iTunes still on "welcome to your new iPhone" even after I'm done restoring it from my backup

I own an iPhone6 64GB and I just noticed that when I connect it to my computer, there's this mysterious "Other" data in my phone which takes up a stunning 25GB of space on my phone. So I searched for a possible solution online and found out that you should restore your whole iPhone to erase that "Other" data. I did that earlier but of course, I synced my phone first for the backup.

And then I'm done restoring my phone from the backup (and my phone works again and everything's back to normal except all my apps and music are gone). I connected my iPhone to iTunes again so I can put all my music back but everytime I connect my iPhone to iTunes, it will just show the "Welcome to your new iPhone page" again which was the page before I restore my phone from the back-up and there's no sync button. Can you help me guys? I just want to get all of my music back. Does that mean that my phone isn't done in restoring from the back-up? Or is that just another bug? Any solutions for this annoying problem? I will be forever grateful if you can help me..

Seriously I'm so ******. I also noticed that the "Other" data wasn't gone!! Apple should release an update fixing this bug because IT IS a big deal! So much wasted space on our iPhones 😠