Write a letter of complaint according to the following situation: You bought a luxurious bag by credit card in a store when travelling in the US. Two days later, you returned it and the salesperson promised to give your money back to your card within 30 days. Now 40 days have passed, yet you haven5t received the refund- Write to the store to describe the situation, express your demand and ask for a quick reply. Please sign your name as Li Fei. （150-200 words）