I think that you misspelt the word three times, Dmilton!
Through our normal investigations, it has been identified that your book order was duplicated on 10/June/11 (October 6, 2011?).
Should there be a comma after investigations as through is a sub conjunction?-- Yes, it makes the structure clearer. But the sentence is rather stilted and
The problem, DMilton, is that not everyone does that and not everyone is from England. That is why it is always potentially confusing and why it is always better to abbreviate the month with letters instead of numbers. That way, you can never be wrong and always be clear.