Asked company to discontinue the services generated bill after that

I was in chennai 3 mnts ago. Living with one roommate. We both took tikona net connection with my user Id. I relocated to Bangalore and requested tikona to close the service which is running on my user Id. Tikona did not closed the service. My roommate of chennai used that service after closer request without informing me. Tikona generated the bill and asked me to pay. I told them I did not use ask my ex-roommate to pay the bill. Ex-roommate denying to pay the bill and telling lie that he did not user the net service. Now tikona going to file the case against me. I want to find actual person who use the service to pay the bill and punish him to be lying. Please suggest me what step should I take.