The intimation letter is a prescribed format, which can be either obtained from local RTO office/consultant or down load from website.
First give a Regd. post notice.
There is no hurry for such litigation. Wait for a month atleast after giving notice and the actions by RTO and Insurance company.
By the time your case is settled, the life tax period your vehicle must expire.
This is the essential term in agreement about registration, what is that agreement, whether it is having legal sanctity are other factors to be considered.
Instead of that you can even try through District Consumer Forum also.
Some times, simple intimation to Police brings miraculous results.
My friend entering into litigation is not definitely a child's play, do not be hurry, have paitiene, build up record of your efforts.