solution for dual registration on same pan with same business address

hi sir
we found the another gst number created for the existing pan number. while registration first we tried the gst it's asked for some queries and replied them after no gst number created . then we go for new form again filed for same name and same this time created. returns filing regularly. but for the previously not created was created after the new one came. here the problem is we getting the return not filed notice for the after created gstn.
q. how to cancel the other reg. no, if cancelled another one is there any effect for the existing tin returns filing

from khadar