I quit the job because of an extra hour work and a family issue

Hi sir, can u help me by giving suggestions pls? I joined a small school as a primary teacher with a minimum salary of rs 11k. Despite working for 2 months, I haven't received the appointment letter; they kept the signed letter. May be that is the code of conduct copy .they took it back and told that will give xerox .but not yet given.They also have my original documents (degree, 10th, PUC). Due to the burden of extra work and late hours, I decided to leave the job and informed my employer within one month of joining.n I told them that until some other new teacher replaces my job I won't leave this job. I told some family reason that my in law unwell .now she has managed with the available teachers and then she told me not to come. Now, the employer is withholding my salary and certificates, demanding 3 months' salary.(she made an agreement with me while joining ) If I pay only she will give it seems. I have drawn only half month's salary which is 5500. I need your suggestions and advice on how to proceed."