I've tried to contact him on twitter but no reply... Looks that there is no chance to recover these funds. Luckily I don't have much stuck there.
I don't think you can able to contact them they have an old issue before about security breaches that end up closing their service.
About what you said above your post this one
https://instawallet.org/w/some_long_codeThat is the security bread and most of the wallets are recorded on archive.org sample this one
https://instawallet.org/w/h5qmpGNTseZ513uiFT9zqFuAvx277m3zgThat's an old wallet so it's impossible that you can still recover your wallet by giving this URL with your own code because anyone can have the same URL by going to archive.org and use that URL to send it to the owner of instawallet.