Nobody has said you are stealing money, is not a question of theft.
But you are asking IC to send you money which you have already told them is not rightfully yours. I am sure that IC want to return money to its proper owner but they owe a duty of care to that person to return it direct to them, not to send it to a third party, which is you.
Also, when you talk about money, you are not clear whether you are asking IC to return the funds deposited or to pay out the profits that have been obtained with those funds. Funds deposited with IC belong to whoever owns that money, so maybe some of it is yours, but the rest belongs to the clients you mention. It would be surprising if IC sent these other persons’ money to you after you have provided proof that it is not yours.
As for the profits obtained from trading, I don’t see IC providing that to anyone. Any profits made by trading contrary to IC’s T&C’s are probably going to be null and void, and I suspect they will say they are under no legal obligation to pay them to you or anyone else.
Maybe you can get some more details from IC and maybe also get the opinion of a lawyer. It would be great to see some more information to support your opinions.