Are the prizes offered by companies to their customers in exchange for purchasing their products, which are given through a draw without the customer paying any additional amount, permissible?

If a person pays the usual price to buy a mobile line without the intention of entering a draw, and then his name is entered into the draw by the seller, there is no harm in him benefiting from what he receives from the draw. This is because it is considered a donation from the selling party, and there is no gharar (uncertainty) or gambling involved.