Airtel — High level of spam calls on my mobile even after being on DND

I get multiple calls a day for bank and car loans, I have made all attempts to ask these people to stop calling, but to no avail. Finally I registered a complaint with Airtel, but no matter what I do - I get a message from them that they can not find the call to my number and close the complaint. Here is the message I get from Airtel -

Hi, while investigating for the Service Request No.[protected] related to DND issue on your Airtel number, we couldn't find the call/SMS records for reported content for shared date. Hence, no action has been taken against the sender. If you are not satisfied with the resolution, contact 198/appellate to raise an appeal.

Looks like airtel is in Hand and Glove with some of these operators.