Airtel — do not disturb calls

I have registered for do not disturb services. How is it that i am still getting unwanted marketing calls. Today i got a call from sobha developers at 3.13-3.14 pm. I also get a lot o[censored]nsolicited calls repeatedly, though i have registered under Do not disturb services for a long time. Where can i place a complaint against such calls, which disturb my work? Is it a problem of airtel or do i look at other operators who may give better services???