This is something that could have been resolved without any stress and give you a warning not to make such a mistake again, but because of their scamming nature, they will not like to resolve the issue. Even if the money could have entered the account using the normal network deposit, they could still use other means to lock your account and take the money for themselves. Just take a good look at what they did: they waited for a few months with hope and believed that you had lost interest in the case, and they moved the deposit to their private wallet and never notified you of the recovery. Something they could have done when you emailed them the first time.

I know depositing on the wrong network is discouraged, especially when a platform warns you of such a mistake. On other centralized platforms, what they will only do is warn you; sometimes they will ask you for some kind of recovery fee, which you can pay via your main account or they will deduct from the fund before they can send it to your account, but at the end both you and the platform will have to settle amicably. Since both the BSC and ETH address always share the same private key (I don't know if it's the same with centralized systems though), I guess it's simple for them to just detect it and move it out; it will only cost them a little extra time.