Is it a fully flex booking? If so just cancel and book again through the Pigsback site. I am not sure you need to be logged in to the Pigsback account. The important thing seems to be that the IATA code goes on to the booking and I am sure Pigsback will be happy for that to happen if you are logged in or not.

I wouldn't get to caught up in it all and just leave the booking and make the claim. The hassle may not be worth the £20 in vouchers??