TT cannot provide such a letter. It is a computer program for preparing your own taxes, not a CPA firm.
Exactly how did you file? You cannot file Single if you were legally married on 12/31/2017. To file as Head of Household, you must have been separated form your spouse the entire second six months of 2017, not 6 months prior to filing the return. You must also have had a qualifying dependent, and meet certain support rules.