GST registration (migration) window shall reopen on 25th June, 2017 and continue to reopen for three months and all the existing taxable assessee registered under VAT, excise law, service tax can enroll themselves under GST.
Earlier the window was opened on 1st June, 2017 to 15th June, 2017 to provide opportunity to leave out assessee’s. However, since still a substantial percent of taxpayers still remaining to be migrated under GST, the government has decided to reopen the GST migration window to give chance to remaining taxpayers.
Also note that your provisional ID will be your GST Identification Number (GSTIN).
Moreover assessees who have applied for Migration & received ARN (Ask Ref No) download Provisional Registration Certificate from www.gst.gov.in wef 27.6.17