Tata Sky — unwanted calls on landline

Address: New Delhi, Delhi, 110018

Getting regular calls from tatasky, every day, sometimes 2 times, and they keep forcing to talk about channels, we are not interested in.
We have already talked to them, nicely saying we can manage our own. But they keep calling everyday, on talking to tatasky office, they say no calls from them.

They keep calling on our landline number, which is surely a privacy issue.

Help us resolve this, because it's getting out of hand and very irritating.