求助 ASOS購買問題

請教板上的大大我在昨天收到一個折扣碼的信件有20%的折扣只有24HR那個
今天想說買一下好了在結帳時我輸入折扣碼有顯示折扣但是在刷卡後折扣就不見了
變成原價結帳
所以我就以我的菜英文寄了一封信給ASOS內容如下
I use the discount code SAVVY20 to display a 20% discount, but a 20% discount when you checkout disappeared. I paid not expected amount
ASOS給我的回覆
Hello,



Thanks for getting in touch about our recent Savvy20 promo.



We have various promos running at different times - because of this we’re unable to amend the value of your recent order.



We’re sorry we can’t help on this occasion. If you have any more questions, please let us know – we’ll be happy to help.



Best wishes,

ASOS Customer Care
他的意思是不能幫我更改，帶我覺得有點受騙的感覺
請教各位大大我有什麼方法可以捍衛自己的權利