If you have any proof that you actually did the work, you have to pursue that. It's not fair that you put forth the effort and were snubbed because of a technical error.

It's a no lose situation. You've failed at this point. If you try and they don't listen, you've still failed.

If you can prove it, you'll get your grades back. Also, they'll know Blackboard is flawed and hopefully take actions to fix it or not depend on it. Since you hate Blackboard, it's nice bonus.

Good luck! I hope you get this worked out.