You may get the attached letter from the NTS, this is the notice letter for the last VAT return of 2017FY.
Every company need to file VAT return by quarterly, and Sole proprietorship need to file it half yearly respectively.
Some of tax payer decided not to do it since there was no transaction at all during the period, but still you need to file as a nill.
You can download all of VAT receipts(세금계산서) and electronic receipt(전자계산서) from the Hometax.
This time, due date is the 25th of January for filing and payment as well.
Please send me an email to email@example.com for any questions.