Bitcoin being withheld

I have 0.309905 bitcoin in my wallet in bitexeo. They are refusing to allow me to withdraw it until I pay them so they can pay some tax on it (7%). however to the best of my understanding, it is precedent to report your btc as regular income and pay backtax the next year. I would even be fine paying the tax out of my sum immedietly after i withdraw it. However I don't have 680 bucks to just toss at it right now. What can I do here to have them give me my assets?