Cancellation of GST registration: submit Form GST REG 18 reply with documents and authorised signatory verification to contest notice. Reply to a show cause notice for cancellation of registration must be submitted using Form GST REG-18, supplying the notice reference and date, GSTIN/UIN, legal business name and trade name, a substantive reply, a list of uploaded supporting documents, and a verification signed by an authorised signatory stating the information is true with name, designation, place and date.