What should I do about having taken money from people without their knowledge, given my inability to return it or confess my actions, so that God may be pleased with me?

You must offer sincere repentance and return as much of the money as you can to its owners if you know them. If you do not know the owner, then you should give it in charity or spend it on good deeds. What you are unable to return is a debt upon you that you should pay back in installments or seek forgiveness from the owners if you know them. If you are unable to pay back or seek forgiveness, then you must have a sincere intention and a firm resolve to return it whenever it becomes possible, while frequently seeking Allah's forgiveness and supplicating for yourself and for the rights-holders.