Perfect, just a few tweaks…. We are so sorry, we need to reschedule your appointment because we still haven't received your documents . You can also say “as the documents have not been received yet”….sometimes the documents don’t go directly to you so you can make it less “personal” by using a passive voice.

You only need to make two changes. 1) You need to use the past tense, "received," because you are talking about the past. 2) The word "haven't" is a contraction. You need to include the apostrophe between the "n" and the "t." It is a contraction of "have not." The two words are joined into one. Then an apostrophe is used to show the missing letter "o."

Hi, see below: We are so sorry, we need to reschedule your appointment because we haven't received your documents.

We are so sorry, we need to reschedule your appointment because we haven't yet received your documents.