Hathway - Unable to return item due to exit relationship

I have closed the account with hathway * months back and have requested the service agent to visit and collect the modem. But no technician had visited my place. Moreover, I kept receiving marketing calls advising me to renew my account. I had to block the marketing calls due to there harassment. Recently I received mail from the company's legal team stating that they are going to sue me if item is not returned. I even filled the device return form on the company's web page and provided an appointment time. But still no technician or representative have visited my place.