Oh no! That's horrible, I'm so sorry to hear that.
I've never had any experiences with them, but I'd suggest trying a general search of tPF to see if you can find any threads relating to CS issues with this store. They have
got to be
blind to claim that the pictures are blur, as your first pic of the line across the back is certainly clear enough to show that there's an obvious issue. You're absolutely not crazy, and they definitely need to let you exchange or return it, or give you a partial refund to compensate for the condition of the bag! They're a boutique that's supposed to be selling something new, so there's absolutely no excuse for sending you a bag in such poor condition without disclosure of said condition.
If you can't find any further info on this store or previous CS problems, I'd suggest taking a few steps: emailing them more times firmly pressing this matter further (take more pictures if necessary and edit them in Photoshop or MS Paint to point out the issues), contacting your credit card company to look into filing a chargeback if the store refuses to budge, and possibly even contacting the Better Business Bureau or similar to report them. This store absolutely cannot get away with selling you a bag like this.
The stain could still be fixable by a leather care professional like Lovin My Bags, but that can be pretty pricey. You definitely shouldn't have to keep a bag in such poor condition as this, so I hope you press them further about giving you a proper resolution, i.e. an exchange or partial refund, or even a return and full refund. (Personally speaking, though, if they can't provide an exchange, I'd probably press for a return and full refund, even if I had to file a chargeback. Their CS sounds atrocious enough that I wouldn't want to keep the bag and let them keep my money, even if I wanted the bag a great deal!) Good luck, and please keep us posted!