I was told by the local post office staff that my letters got lost for their mistakes. 和 The local post office staff told me that because of their mistakes, my letters got lost. 个人觉得前面的更专业。
My local post office staff told me that, because of their mistakes in the work, my letter was lost 或者 The local post office staff told me that because of their mistakes, my letter was not lost. 希望采纳!!!!!