You should not be compelled to give your personal contact details to a seller in an ordinary purchase.

If you are compelled to do so, just walk away and do not complete the transaction. Ordinary information, like your credit card information and contact details, may be asked for to authenticate payment. But in most cases, your personal contact information should not be asked for. It definitely should not be made compulsory.

Refers to a situation when someone, such as a lawyer or public official, has competing professional or personal obligations or personal or financial interests that would make it difficult to fulfill his duties fairly.

Many government organisations outsource their work  to private firms and there is often a conflict of interests, when the private firm misuses the powers and information they have to further their own interest.

law of defamation & malicious prosecution

The book on the law of defamation and malicious prosecution by V . Mitter is fairly comprehensive with details of complaints and defences. It explains the difference in English and Indian law, civil remedy, libel and slander. This book is very popular, the first edition was published in 1954 and the latest edition , published in 2008 (and reprinted in 2009) is revised by Justice K . Shanmukham, Former Judge, Madras High Court.  The detailed contents make it is easy to refer to a particular section and check the legal definition.  An easy read even if  you do not have a legal background.

Publisher : Universal Law Publishing Co.

You can draft the notice yourself or avail the services of a lawyer.
The notice should be addressed to the person or company against whom you have the grievance.
The notice should include the cause that compelled you to send the notice.
It should also mention prior communication with the recipient regarding the cause of notice.
Offer the recipient a reasonable time say 30 days or 60 days to settle the matter by negotiating and by performing the desired action.
Specify the  time in the notice for either fulfillment of your demand or giving reply
Sent it through Registered AD post or any other trackable method. Keep a copy of receipt of post office as well as notice.

You can send personally send the legal notice without lawyer but it is advisable to ensure  that  you draft the notice meticulously, in such a way that it is not too long but still contains all the material relevant  to the dispute.

LIBEL
Published material meeting three conditions: The material is defamatory either on its face or indirectly; The defamatory statement is about someone who is identifiable to one or more persons; and, The material must be distributed to someone other than the offended party; i.e. published; distinguished from slander.

Published could be online, in the print media or broadcast on TV, radio

When you ask them how much they are being paid, you are  asked to provide proof of their activities.

Online, you lose both  your money and are issued gag orders.