I am writing this letter to you that our company has recognized the letter which you have purchased the company's products and you will get three days.
I am writing this letter to let you know that. Our company was aware of the letter that you have purchased the product of our company. You will receive another three days.
I am writing this letter to let them know Our company has been aware of the letter that you buy product of our company and you will receive the goods again 3 days.