Damn man, that sucks :/. I know someone else too that got banned for hijacking today.
Tips that i do:
When you are trading the stuff to your main, always put items from your main into the trade so it doesn't look as suspicious as if there was nothing.
After the trade is done, say "Thanks Dad" (I don't really know if this works, but its best do it, than not.)
Since you used a VPN, though you should have emailed them saying that someone else had access to your account and you couldn't of done anything to stop it.
You can also try emailing jagex pretending to be a parent saying that your "son's" account was hacked.
If you do need a new VPN, i could possibly hit you up with one. Just pm me.