Update today from our contact with the Financial Ombudsman a month ago:
"We’ve had a look for GTP Capital and Oasis Capital on our systems, unfortunately we’re unable to help you investigate this case. GTP Capital wasn’t on our database at all. We searched them on the internet and found that they were linked to a company called Oasis Capital (UK) Limited.
We found Oasis Capital (UK) Limited on our database, however they aren’t a regulated business. Since they’re not a business regulated by the Financial Conduct Authority – we don’t have the authority to look into complaints against them.
I know this is frustrating news, but unfortunately there’s nothing further we can do. It may be best for you to seek independent advice to explore what other options you may have.
I’m really sorry we’re unable to help you on this occasion.
Yours sincerely
Kitan Eleyae | Investigator
Financial Ombudsman Service
Exchange Tower. London E14 9SR"
So, as their Facebook page still stands (and cannot be commented about), we're on to try something else. Our credit card company wasn't at all helpful (they see options as "gambling" so won't touch it, and of course say we gave all our details to GTPcapital so it's out own fault).