Seems weird/stupid that you contacted the SEC. You might as well contact the Securities Bureau of the Japanese Ministry of Finance whilst you're at it.
Quite strange indeed, many seem to think SEC deals with brokers globally. Financial Conduct Authority of UK is where he should go as that broker is regulated by them, maybe also the Cyprus Securities and Exchange Commission but I doubt they'd reply.
Never had problems with Aussie brokers never had problems with US brokers.Had issues with some UK cheap fund managers.Would never open UK brokerage account.
SEC is not involved just because foreigners might trade US options. SEC is a U.S. regulatory agency, it does not have any authority over a foreign broker and its relationship with a foreigner.
When you say Aussie brokers you mean equity or OTC FX / CFD are you aware that in AUS regulations if a OTC broker goes belly up you the client becomes a creditor the ASG does not protect you , it only applies to Equity, In that regard UK FCA is better for traders Do search on Aussie while label called Sonray Capital Markets DO a search on Alpari UK
The kind of products they offer is irrelevant. What is relevant is where the company is registered and under which regulation it operates. The website states at https://exante.eu/company/ : MFSA is the Malta Financial Services Authority and CySEC is the Cyprus Securities and Exchange Commission. Depending on whether your account is with XNT or EXT are these the authorities where you should send your complaint.