Something which is going to be difficult to prove, after all stake did not really scammed the OP since this is a bonus problem and there could be many explanations possible, like a change in the size of the bonus to old clients, technical difficulties, the OP not qualifying for a bigger bonus due to the games they played during that week and an interminable number of reasons that could be used to explain this issue away, so unless he can demonstrate that whatever bonus he was to receive was in fact stolen by someone at stake there is not much of a case here.
You jump to bold conclusions very quickly. If he didn't receive its last weekly bonus through the normal telegram link but through a drop to its vault there is obviously something wrong with his account. It seems there is an error somewhere or he has been
shadow banned from periodic bonuses by Stake without any notice. Moreover with 600 USD wagered in a week he should have got some cents at least. Shadow banning is not a professional neither honest practice from a big casino as Stake. If they wanted to ban him from bonuses they should have noticed him before.