Such an experience is really painful, especially given the amount involved. 
May be the system is suspecting a scam or fraudulent activity which they have not cleared off, but it looks some how odd to me to deposit 12k immediately into an online casino and immediately rush to wager huge amounts after your first win, which seems like you are testing the platform after confirming it with a win, then quickly move further to bet 5k in another game which was declined with it seeming your plan of deposit has been trampled upon because of that and you want to withdraw your asset immediately. I pray this gets resolved soon enough. 
Was never aware of this earlier before now.  So if I fund my online casino account more than I planned to and intend to withdraw the surplus immediately, I won't be allowed to do that? Unless I wager up to the deposited amount first. 

Not really I'm confident that they can resolve this issue, based on OP's post there are loopholes in his case, Rollbit can easily address this just like all the other issues, and every issue resolved in the scam section can be considered good for the reputation of a casino, some of the accusations are based on complainants' failure to follow the TOS of the casino, and some are fake accusation, it's just annoying to see two threads on one casino one is an announcement and the other is an accusation.

What casinos are you playing right now, and how many terms of service or rules you've read in the casinos you're playing, that's the trouble with players they disregard the most important part of the casino, which is not the games, it's not the features but their terms, disregarding this will put your account in trouble.
That is why I question TOS that is incomplete no TOS or not visible TOS as if trying to hide its TOS, when a casino is hiding its TOS they want to trap gamblers, but one of the basic rules of casinos is wagering requirements whether the funds come from the bonus or from the deposit.

Have only used few and off recently playing with Sportybet, read there t&c but never understood this part fully until now, I can see what they throughly means by the below statement.

OP, I agree to the speculation that your account has been flagged with money laundering. How long have you been playing to online casinos? If long enough, you should be knowledgeable with most casinos terms with wagering requirements. In spite of that wouldn't it be better if they confronted the OP with his/her violation? Because I also think that it is the professional way instead of just ignore him/her

To be fair, OP did try to wager $5K more, only to be limited to $200 as the max he could stake. I think this is what pissed him off to withdraw all his funds from the casino. I myself wouldn't want to wager small amounts $200 in so many matches just to meet the wagering limit, yet I have about $12K in my account.

Did you come up with this nonsense yourself? 

yes, almost on average, the casino team does not respond to any accusations and reports in this forum and often ignores them even though they should respond so that everyone knows the casino that the casino is behaving professionally, at least a little respect the OP who made these accusations even though the OP also made mistakes at least the casino responded to this, well I'm not taking sides with anyone, basically this is all just because of communication and lack of reading where gamblers should before playing read the rules and requirements at the casino so that problems like this don't happen.

You will not be in that situation if you understand the logic that you need to wager once you deposit, it's a basic rule of majority casinos you cannot just withdraw the excess or portion of your deposit, because in the first place why would you deposit an excess amount?
It's understandable even if this rule is not in the FAQ because there are very few or no casinos that will allow a withdrawal without wagering.