I think you need to first clarify if you got a "legal notice" or a "summons." A legal notice is typically sent by a lawyer (or sometimes through the individual / company directly). A summons is issued by a court notifying you that a complaint / case has been filed against you and further informs you by whom the case was filed and under which legal provisions. It informs you that you of the name of the judge and the date on which you have to appear before the judge. Typically such summons come stamped with the Judge's stamp, while a legal notice comes on the letterhead of the lawyer /company / individual issuing it.
f it's a legal notice you can reply to it or ignore it. I would suggest you reply. If it's a summons you should appear on the date and explain to the judge that you have nothing whatsoever to do with the case, and if he/she requires you, file a formal written reply.
As for filing a FIR, why do you want to add to your hassles? Firstly, they have not committed a criminal offence (unless they have threatened you with violence or something like that). Secondly, the police will not file any such complaint (and will view it as being frivolous) and instead hassle you. If anything, should the harassment continue from Airtel, issue a strongly worded legal notice against them, CC it to TRAI. As for consumer court, you may have a case (though not a strong one) for harassment. But you will soon fine that going to consumer court is much more of a hassle than dealing with Airtel! :Shabbo: And moreover, after fighting the case for a few years you may get a couple of thousand rupees as compensation (but have spent more on just the petrol in having to go on every date!)