Your case file shows you tried to withdraw a substantial sum based on the balance. The broker reply you posted in your case file claims that there are large floating losses, leading to a much smaller equity. Without seeing the FULL statement which shows balance, floating P/L from open trades, and final equity, there is no way to tell if the broker is properly blocking the withdrawal or not.
Here is a real world example I grabbed from an FPA Performance Test:
Summary:
Deposit/Withdrawal: 666.57 Credit Facility: 0.00
Closed Trade P/L: 777.61 Floating P/L: -849.38 Margin: 198.13
Balance: 1 444.18 Equity: 594.80 Free Margin: 396.67
The owner of this account CAN NOT withdraw more than $396.67 even though the account balance is $1,444.18, because there is a floating loss of -$849.38.