Request suggestion on tax related issue from one transport contract service establishment

The establishment M/s Mohan Road Lines, engaged in the business of transportation on contract basis for various entities under the Proprietorship of Mr. Mohan V until October 2012. On October 2012 the proprietor got expired. This establishment had tie up with Mangalore based M/s Sri Ganesh Shipping Agency for their transportation contract and had a flourishing business and it reaped huge profit as per the feedback received from the authorized person through court. When enquired about the licence of the establishment we got the feedback from the Gram Panchayat office that ther is no registration licence issued or reneived to this establishment from 2014-15 onwards. Not sure whether this establishment had registration licence before 2012-13. Also not sure whether amendment has been done for change in proprietorship as at present different Proprietor name Mr. Murthy displayed one establishment name display board. This establishment had its branch at Hospet of Bellary district and reaped huge profit there also. Not sure whether the establishment not had registration licence for the Hospet branch also. Presently this establishment not got registered with GST and there is no GSTIN Certificate issued in the name of this establishment as per written conformation from Commercial Tax Department. Above information it bring benefit of doubt that the establishment had not done Annual filing of Tax returns by declaring the total income of the establishment from day one as the establishment itself not got registered and procured licence. Based on above information kindly suggest to which department we can approach to put an enquiry for investigating the annual filing of tax returns done by this establishment or not.