Dollar Tree review: manager rude

I came today and Sonia who was the manager today at 12 pm she gave me the worst customer service I have ever had in my life I can't believe she was the manager because she gave so bad attitude, the place was busy I had few coupons, it's not the first time I buy there with coupons and I was sure I can use it because I did in other dollar tree so I told her probably you don't know how to scanned and she keep said it's not for these the coupon said it's for these so I told her you're so rude I'd like to speak with the manager and she saw me her id she was the manager omg seriously the manager should be the person with the best attitude for the customer even if the place is because if you can't work under pressure you should get another job because the customer who is pay you check, you should take care better your customer service is so bad