Harrasment by Hathway

I'm extremely frustrated with the Hathway people. I've recently stopped using their service as I've moved to a different place. From then, I've started getting 6-10 calls a day.

I've politely replied to them, begged them to stop calling, shared my frustration, mail their nodal officer and even shared it on twitter. Everyone of them says they're adding me to DND mode but its just not happening.

It's been a month and I'm seriously getting frustrated and losing my mental peace. Typing this rant as I've woken up by their call on a sweet Sunday evening.

I mean doesn't these many calls come under just plain harrasment? Don't they have any sense of privacy or personal space? The most frustrating part is their Nodal officers' numbers don't work. Please suggest ideas or ways by how I can make this stop.