Is the money recovered as a result of breaking a headphone while trying to expand it unlawful, especially since the lawyer advised claiming that it was not opened in order to recover the money?

It is not permissible for the buyer to lie and claim not to have opened the item. If he does so, and the seller refunds the money based on that, then the money is not lawful for him, and it falls under consuming wealth unjustly, as Allah Almighty says: "O you who have believed, do not consume one another's wealth unjustly." And the Prophet, peace and blessings be upon him, said: "All of a Muslim is inviolable for another Muslim: his blood, his wealth, and his honor," and "Whoever unlawfully takes the wealth of a Muslim man will meet Allah Almighty while He is angry with him." He must return the money to the seller or seek his forgiveness for it.