This side Ashish from Aarti Accounting Solution. If you had apply for Gst Registration Certificate and your application got cancelled then you may check the same on Gst Portal by mentioning your Temporary Reference Number (TRN) here gst.gov/trn , also fill the captcha and then click on proceeds. Thereafter you will see a new page where you can scroll and search for "Application for Filling Clarification". After this you can enter the clarification code which you had received via by gst department on your mail.
After following the whole process you will surely get the reason why your gst application was rejected by the Gst Department.