Hathway — Hathway- Getting multiple calls even after returning modem.

Address: Chennai

I have closed the connection and returned the modem, still I am getting multiple calls daily for past 40 days.
I explained them so many times but they always acknowledging and doing the calls daily.
I am working in second shift, daily morning they are calling, disturbing and giving mental pressure.
Daily thrice they are calling and even disturbing my entire family.
I have activated DND in network and in Hathway and warned they I will give police complaint. I am not sure what to do.