The neck pillow I ordered was supposed to arrive by March 1st, but it hasn't, so I'd like my money back.
この場合、次のような言い方ができますよ。
ーThe neck pillow I ordered was supposed to arrive by March 1st, but it hasn't, so I'd like my money back.
「注文した首枕は3月1日までに到着予定でしたが、まだ届かないので、返金してほしいです」
to arrive by で「…までに到着する」
I'd like my money back. で「お金を返して欲しい」
ご参考まで!