I will create a scam accusation thread against Betja. What's the best place to do that, and do you have any recommendations as to what I should include in there?
Scam accusations should be posted in the appropriate sub board, here >
https://bitcointalk.org/index.php?board=83.0.
You can always follow the scam report format as shown in this example:
https://bitcointalk.org/index.php?topic=260073.0Make is as clear and clean as possible. Include all proof you have, including communication you had with the support, email exchanges, links to your deposits, betting history, proof of missing withdrawals, and whatever else you think might help.