Am I entitled to refuse a refund and demand that the store purchase the two devices at their original price after their long delay in delivery?

Contracts, such as sales, are binding on both parties, and neither party has the right to unilaterally dissolve them except with the consent of the other. Rescission (Iqālah) is recommended, as the Prophet (peace be upon him) said: "Whoever rescinds a transaction with a Muslim, Allah will forgive his stumbles." Therefore, the seller is not permitted to dissolve the sale except with your consent, and you have the right to refuse the dissolution. It is also not permissible for him to stipulate an increase in the paid price in exchange for the dissolution, because rescission is a dissolution, not a sale, so it is not permissible except for the original price. If the sale is a Salām (forward) contract, it is not permissible to sell the debt of the Salām contract before taking possession of the object, nor is a penalty clause for delay in delivering the object of the Salām contract permissible. If you choose to dissolve the sale, you are only entitled to the price you paid, without any increase.