As far as my knowledge goes there are two types of defamation case, Civil and criminal: Correct
First, send them a legal notice and seek damages/compensation from them to cover the loss suffered by you in terms of the dent/damage caused to your reputation.
If they do not pay you the damages despite this notice, file a suit for defamation. To do this you will have the take legal assistance from a local lawyer. This case will be filed in the lower curt. Lawyer's prof. fee varies greatly from one lawyer to the other and this case may take anything between 2-4 years till it's final disposal.
The above is all about defamation as a civil wrong and the remedy against it.