Dingtian withdrawal issues

I'm not sure my case is Scam or not (hope is not). But I have waited for 2 weeks, and now their supporter keep silent every I provide my information. I and my friend deposited on this platform about 66k USDT and withdrew successful 2 times (50 USDT per time). About 2 weeks ago, I withdrew 17k USDT and the issue start here. First time, their supporter ask me to pay tax 10% for all balance and I transfer about 18k USDT for it (my friend and me transferred together and made it wrong.