英语高手进来看一下!谢谢

一楼 二楼和三楼的也太强了吧，so 和 because 在句中是不能连用的吧？

we're so regretful to tell you that we couldn't modify the freight in time because you didn't inform us before payment.But we assure you that 1€ discount is still working ,please don't worry .
其他的自己搞定，别犯那些无谓的错误。我建议你看看商务函电，用的必须的专业词语，不要把口语也弄上去，上面很全的。

I’m sorry, because you do not notify us before payment, so we could not even if you modify the freight. But do not worry, we promised to give you 1 € discount, it would not go back, if you wish, we the 1 € refunded to your paypal account or wait until the next time you come to buy things, what this time give you a discount. your opinion? look forward to your reply

I’m sorry. because you do not inform us before payment, so we didn't revise the freight fee for you. But do not worry, we promised to give you 1 € discount. we the 1 € refunded to your paypal account as you wish or wait until the next time you come to buy things. What's your opinion? We