Can company file case against me even though I have served the notice

I worked in an it firm in. While joining I signed an agreement in which it was written that if I leave the company without serving the notice period i.e 30 days while in probation then I have to compensate them with the salary of the notice period plus amount equivalent to three months gross salary. But there was nothing mentioned that if they fire me during probation then they will also pay me the same amount. Now that I've joined a new company I'm getting calls from previous company that they are going to take a legal action. Now my question is that are they liable to file a case against me for this, what could be the conclusion and is there any way out.