Sorry if I'm wrong here,
This situation can't be solved if you can't provide the proof when you said your 0.006 btc credit is gone. Does this online casino can view your balance history? So you can know where's your credit going
Let me enlighten you with what actually happened :
1. Every new account is credited with 1000 credit which is $10
2. Everyone could withdraw it once it hit 10000 credit or over
3. OP made an account and turned it into over 10000 credit
4. OP withdrawed 10000 credit and has some credit left
5. OP's free leftover credit dissapeared after he withdrawed the 10000 credit
6. Dicedice added rules to which you can only withdraw maximum of $100 which is 10000 credit if you play with the free 1000 credit given to you by the house