Form V-17 received from Mhagst PT Department

Hello Team,

I am a Mumbai based sole proprietor and I do not have any employees. Since inception in 2016, have enrolled myself for PTEC professional tax and have duly paid 2500 professional tax every year. 

Almost every year I receive email from Mahagst department that I am liable to enroll and I need to pay professional tax. In return , I send them my PTEC certificate and all the paid challans. Also mentioning that as I dont have any employee I am not liable to register for PTRC.

Today I received an email from Mahagst which is an attached word file with subject "URD PTRC  FORM V PHASE VII". They have mentioned again that I have not enrolled and I am liable for paying late fees. They have also mentioned its a show cause notice and have asked myself to visit there office on a particualr date and time.

If my understanding is correct, Form V mentioned in subject line is for PTRC which I dont think I am liable to enroll for.

Should I need to take this email seriously? What should be my next Plan of action? Has anyone else received such email based in Maharashtra?

Pls. help and guide.

Thanks in advance!