Post about your problem on their twitter. Then google "ExtStock" and leave negative reviews for every single review site you see. Also, click on their username here and give them negative reputation. Then email the FCA to file a formal complaint here: https://www.fca.org.uk/report-scam-unauthorised-firm-individual

They told one scam victim to email them a scanned and signed letter asking to undo the trade from crypto to USD. You see, the way one of their scams works is they let you trade crypto into fiat, but then when you try to trade back they say you need a special and obscure traders license, which is funny because you legally don't need a traders license in the UK to trade crypto into fiat and back. They are scamming you. They are trying to steal your money and they're hoping that they can keep you quiet long enough so they can continue to steal other people's money as much as possible until this whole thing comes crashing down on them. It's your duty to warn others and report this to the police/UK authorities and the cryptosphere. This is obviously some kind of money laundering/pyramid scheme/fractional reserve scam and it needs to burn to the ground. All "employees" should be in prison. They've broken numerous crimes.