* Subject-verb agreement: "Generosity and thoughtfulness" is a plural subject, so the verb should be "were," not "was."
* Capitalization: "Thoughtfulness" should be capitalized since it is part of the subject.
Here's the corrected sentence:
"Your generosity and Thoughtfulness were appreciated."
You could also phrase it in a slightly different way:
* "Your generosity and thoughtfulness were greatly appreciated."
* "We appreciated your generosity and thoughtfulness."