My ex-employer have sent a legal notice for breach of bond

I was working with the company for 1 year and left without giving 3 months notice period as was required in the bond. I had signed a bond of 2 years in which I had to serve 3 months notice period without payment or pay 3 months salary in lieu of the same. I was on probation for the same period of time. While working I came across several issues which are: 1. They was no sanitation in the office as in it was infested with cockroaches. 2. They was no training given for the post I was hired. I was directly given a project and told to execute it. 3. They were giving PF to certain employees but I was told that they didn't have any PF or EPF policy. 4. I was asked to do jobs that were not part of my job description. I had to write a project for director's son and among other things. 5. They hadn't given my 1 month salary and were not giving any reasons of the same even though I had asked them several times. I need to know what I should do now. Should I reply them? Would it be better if the case is taken to labour court? Thanks