I bought a "brand new" K800i off Amazon last week from a 3rd party seller.

Found out its a chinese copy and want to return it, have contacted seller to ask if i can return it and how i go about doing so... Have not had a response since early last week (when i sent the original query)

I now think i should make a complaint about this seller to Amazon, how do i do so?

I would definitely complain to Amazon. They pay the seller, so might be able to chargeback the money on your behalf.

I've never had to do this so not sure of the process, but I would definitely drop them an email.