Still didn't receive the BTC in exchange of your BTG? If you haven't contacted the support yet, I think you should do so support@changenow.io
@ChangeNOW_io seems to be active on twitter answering people to send an email to support and will be assist further. Since you've mentioned that it was endorsed by @bitcoingold, maybe the team checked how trusted the service is.

@OP didn't update here, I wonder if he used the site or just waited for an exchange.