What is the ruling on using discount codes and free rewards offered by some companies upon purchase, when a merchant buys his own goods from himself using these codes through multiple phone lines to obtain free amounts?

A person is not permitted to buy from himself, because a sale is the transfer of ownership from the seller to the buyer, and this is not achieved by a person selling to himself. Consequently, whoever buys from himself is not entitled to the reward allocated to buyers via commercial platforms, because these rewards are for stimulating real sales and not for deception and taking money by false means.