The saddest thing is that this "advance fee scam" was described 1000 times before. For example: https://bitcoin.stackexchange.com/questions/103891/is-it-normal-to-be-asked-for-an-advance-fee-on-a-withdrawal . Although on second reading of your post, they tried to obfuscate a bit with top-tier thing. Still, why would you pay the tax to someone else than IRS (and Darthcoin wouldn't pay even them :))?

The scam possibly hasn't ended yet: someone may contact you promising to recover your money. For a small fee, paid in advance, of course. Please don't fall for it.