Vodafone India — overcharges than usage

Address:

Krishna, Andhra Pradesh, 520001

I converted from vodafone to airtel i last year and i used vodafone for 21 days, but i received a bill of 437 (Actual plan 299), in the initial month i received a bill of 270 because i used it for 22 days, then how can you charge 437 for 21 days usage? Regarding this i written a mail and asked them to call, they havenot called and a maximum of 2 calls i received and the person replued that his higher official will contact me, after that i havenot received any calls but yesterday i received lega notice regarding this, even then i contacted the person which having mobile number in the mail, he too had not received the call, without having proper communication how you send me a legal notice?