Stake asked the OP to provide his source of funds statement. They have suspended his account and requested for those documents. OP will be able to access his account again if he can successfully go through the verification process.
If it is so, they're stealing from OP. They have no right to keep his money regardless of whether he can prove it was earned by him through mining or whatever else.
Imagine that he was given this money for free and cannot prove that it's legit, it's still his money. No company has the right to act like a judge and jury and steal that.
I don't know how Stake will approach this but there's only 2 legal ways. Either they accept the money, or return it back to OP.
^Since then I did not play Stake when I saw more complaints against them even though they have a lot of promotions.
You are definitely right, they have no right to freeze an account that has money not unless this was on the ToS which is OP there is nothing to do because upon opening the account he agreed with the terms. Stakes should not do this because it is ruining their reputation, a warning could be the right approach to this and if OP can not do the requirements at least withdrawing the fund is much better. So my question is, if they are doing this to other users, what will they do to the banned account that has money? That money does not belong to them.