More Viagogo woe :(

A couple of weeks ago I purchased two tickets via Viagogo for the second leg of the Copa Libertadores final as part of a trip to Argentina.

The tickets cost about £200 each in local currency, with a £150 service fee.

I got confirmation that the tickets would be delivered a day or two ahead of the game, which is scheduled for 24th November.

I bought the tickets right after the game was confirmed (it is a massive local derby) and since then hype for the match has gone through the roof. You can't now buy a ticket for the game on Viagogo for less than £800 in local currency.

I feared this might cause problems, and sure enough, yesterday I receive a message from the seller saying he needs me to cancel the purchase because the tickets are actually non-transferrable.

I point out this is likely not the case because hundreds of tickets for this game are being traded.

He comes back and changes his story. He now wants another £400 from me to release the tickets, because he's realised he sold them for under market value (albeit still a ridiculous mark up on face value).

I've not responded to this, and have reported him to Viagogo with screenshots, but no response so far.

Am I screwed? Will Viagogo deliver me tickets at the price I paid regardless of what he does?