Employment is deemed a "Contract" between two or more mustually & voluntarily Consenting Adults per India Contracts Act 1872, hence "Obligatory" and "enforceable" on the contracting parties. Any breach of theagreed to Terms of Contract will call for corrective actions failingwhich, may lead to enforced Obedience by the Non-Conforming Party/ Signatory.
Whether you were "Employed-on-Probation" is a relevant Factor and in case you were on still-on-Probationary Period you could "call-it-quit" without notice period as has been the "settled" practice/ precedent in Employment-on-Probation case.
If you were already "Confirmed" at the end of Prescribed Probationary Period or the Probationary Period was "shortened", asit were at the behest of the Employer and thereby you became a" Permannet Employee against a Permanenet Position/Post", and a Revised Set of Co's Rules applied to you namely "Giving Notice Period" as prescribed in the Confirmation Letter, you were "obliged" to Serve the Notice Period irrespective of "Inconvinience" mentioned by you and it is "Self-evident" from your post that you did not exert / excercise any Discretion" when you hastily decided to report for "Duties" in another Establishment without "getting properly Relieved" / from the Establishment you were/are employed on their Muster-Roll which amounts to "Dual Employment" which in itself is Unlawful Act on your part, hence null & void attracting thereby ?remedial legal action including Punishment and Penalties.
In the circumstance, it is surely "a matter of concern" for you and as far as "threatening" of legal action agasinst you is concerned your" current Employer" (as refered to by you" may be " charged with "illegal poaching" as commonly understood.
It is expedient, therefore that you revert to your First Employer requesting them to gracefully "amicably " settle the pending matter and "relieve"" you of your Duties/Employment, propely including " Discharing you From their Muster-Roll, formally/offcially closing the somewhat bitter "disposition" as it were.
Kritarth Team,
Bengaluru Service Office
16 Feb 2019