とりあえずこんな感じでメール送ってみました。

Sandra,

I am referring to the J. S. Bach CD set by B.M.S. that I purchased from
your company recently.

I noticed the two CDs (MM4145-2 and MM4146-2), which are supposed to
contain "Sechs Partiten BWV 825-830", actually contain the same contents
as MM4131-2 and MM4132-2 "Das Wohltemperierte Klavier Teil 2". I would
appreciate if you could send me the right CDs for "Sechs Partiten" at
your earliest convenience.

Regards,
XXXX