June, 20, 2020I am writing this letter to ________________ （投诉）the quality of the phone I bought last Tuesday in No. 1 Department store. The phone always______________________ （黑屏）. I called the ____________________ (售后)， but the problem was not solved. Therefore, I have sent back the phone and the receipt to you and strongly insist that you ______________________ (退回我5000元) as soon as possible. I would be ______ （感激的） if you could have this matter settled.