What action can be taken for threatening calls from Tata Photon

i was using tata photon device for internet. in july- aug i given them a complain regarding the speed issue and being over charged in bill. they given me request no, and ask me to wait, after a wait they never resolved my problem and i decided to quit the use of their services for that a had given them a phone request and recieved a request no. again. Now today i recived a threatning and abusin call from one lawyer asking me to pay the bill for the months when my internet connection was not in services. And he given me a half n hour time to make the payment or else they will issue the warrant n all. I am really not getting the method they are working kindly guide me to deal with the issue.