My challenger has a full inbox and I need to contact him. What can I do? The due date is coming soon and I haven't heard from him in a while.

Visitor Messages work.

I've tried that actually. Still no reply.

You'll probably just going to have to take it as a forfeit on their side then. Just how it goes sometimes.

Understood. Is it possible that i post the anim on the battle zone and wait for my opponent to respond atleast about a week? Or would I be able to repost the battle?

If you're patient enough, maybe you can wait for him for several days ahead after the real deadline before taking the forfeit victory.

But before then, don't post it first, and you're only able to post it just once. Both your battle parts should be posted together in a thread at the same time to prevent bias.