Employer Refused To Give Back My Certificate

The most practical step would be to serve a Notice, preferably, through an advocate requesting for return of the Certificates. The Notice could be served by Registered post and copies may be endorsed by fax/e-mail. The next course of action could be decided on the basis of their response or lack of it.
The detaining of the certificates and demanding payments for returning them amounts to the criminal offence of Extortion.
Even otherwise, the employer has no power or right to keep certificates for realising the alleged Bond money as decided them; even if any such amount really realisable, they need to adopt the due process of law - there cannot be any unilateral enforcement keeping the certificates in bargain.
This is a wide spread abuse. It is unworthy of the educated persons to succumb to such abuses.

Senior,
I m having staff ID card & for attendance we use thumb reader is that enough???

That should be proof of being an employee and time records of attendance can be accessed since you used thumb reader.

Dear seniors,
I recd a registered post from my previous employer the letter as follows
u r absented from ….. On date.without proper intimation & later we understand that u r sick
we informed yr spouse advise you to come here & settle all yr work & bcz all yr work is in critical condition which u left
u r unauthorised absence caused lot of issues & we again advise you to come here & complete all the pending works failing which suitable disciplinary action as deem fit shall be taken against you as per our rules & regulations
i send my resignation through Regt post & i informed properly to them to office landline number & try to inform one more person who incharge of admn dept.but that person didnt attend my call(i called nearby 20 or more time).they alloted me a new work (which means i transfered to new dept & handed over all my work to another person).according to their letter i dnt have anything to settle & handover
pls advice me what should i do now

The registered letter from your employer is a pressure tactics.
Do not succumb.
Send them a polite registered letter asking for your original certificates back.
Summarise the issues which you have with company-like non receipt of pay/with holding of pay etc.
If they do not return your educational certificates,lodge FIR against the person to whom you handed over educational certificates.
Take suitable legal advice with a local lawyer.
Do not get scared by letters and take action from your side.

my spouse advised me send a doctor certificate for my resignation. is that a good idea ?(i dnt wish to go there again & meet those persons & work some more days)i m presently working with some other company.hence that idea is a advisable one?

Seniors,
i prepared a letter stating that,i m not able to come there immediately due to my illness&i informed properly to the proper person & i dont have anything to handover bcz anyone didn't handover anything to me according to yr letter.kindly return my certificates at the time of my visit & pay my salary due
is this ok or i have to add any other point

Dear sir,
kindly give me a format for asking my certificate in a polite manner

Dear seniors,
after a long gap tomorrow i am going to meet my ex employer to ask about my certificates.i already contacted them through phone.but they said the HR is in long leave after his joining only they can think about releasing my original certificates.what shall i do?
i have to please them or fight????
(it is nearly six months from resignation)
pls Help