Bitstarz is one of the shadiest casinos out there. It's pretty much their entire MO is to steal players balances, and when they don't, they like to try to (e.g. weaponizing their KYC for the sole purpose of making sure people don't withdraw or get frustrated and gamble away their money.). They seem to be well promoted because they are able to offer a super generous affiliate program, so the 100000 "casino review" (affiliate farm) sites out there love promoting it.
The good news is bitstarz tries to keep a thin veil of legitimacy, so you can use that in your interest. Link your story to their bitcointalk feedback, contact all the review sites, their licensing etc. And in the mean time do
not gamble or lose your money, as it's a process that (intentionally) takes a long time. Generally if you're annoying enough, they would rather just give your money, they prefer to steal from people who keep quiet.
And for next time, try play at a casino listed here:
https://cryptogambling.org/ (it's not a perfect list, but it's by far the best one I've seen out there)