You have posted that "Now the issue is that my manager and his boss are continuously harassinge with lots of work load and keep mailing me that my performance is not up to the mark any more and I am not stretching for long hours as well as I am not working on weekends also if other team members come etc."
If such comments have been passed on to you in writing these go against the company. You may forward these and keep these in a secured file, in your personal possession. You may also secure your attendance record from entry and exit register, bio metric card, online attendance, appraisals, appreciation and stinking mails, awards/rewards, mementos, increment letters, CSR activities etc
The line management can comment that performance is not up to the mark if indeed performance is not up to the mark. The performance is measurable against measurable parameters. What are these measurable parameters? Forward these criteria to your personal email id registered with company or obtain its print out along with your performance from your DOJ till date. If these criteria of performance are available then you can also measure your performance and rate it.
Each company has/should have its well defined internal grievance redressal system. You may report the incidences in gentle tone to good offices of your appointing authority, MD/CEO/Chairman, Company Secretary, with a copy to Head-HR, in writing under acknowledgment and keep the hard and soft copies. You may conclude that you have been working sincerely (highlight your achievements and discipline and decorum you have maintained) and that you have submitted notice of resignation in line with policies of the company and even during your notice period you are working sincerely and delivering results ( mention the status reports) and that you are concerned and disappointed as there are deliberate attempts to malign you while at this time both you and company should put in concrete efforts to separate at a good note and carry forward the rapport and goodwill during the period of association. You may mention that you have made sincere efforts to ignore the incidences and resolve the matter on your own and by the intervention of superiors (do take with some senior who favors you) but there is a cold response, and it has become almost a daily routine that stinkers are being shooted at you and you are being subjected to humiliation. Hence you are seeking intervention of good offices to ensure that congenial working atmosphere is provided to you to enable you to complete your notice period peacefully. You may mention your working hours, off days, as described in your appointment letter, standing orders, and employee rule book, and any email HR policy of the company. If you have worked overtime this is the time you should express OT for each day in office in writing and build favorable record. If the good offices are not able to satisfy you may minute each transaction. You may mention that certified standing orders/employee rule book has not been supplied to you (if true) and may please be supplied to you as ap.
It has somehow become a trend that the employee who has decided to separate be subjected to torment, insult, humiliation and somehow to build some flimsy ground to deny honorable and pleasant exit and probably to deny some or the other benefits. Might be that line management/HR is not competent/resourceful to find replacement. Might be that promoters either encourage it or they turn a blind eye and deaf year to such incidences till the suffering employee shouts.
You may remain vigilant and amiable. If the situation worsens everyday, you may submit the reminders to good offices. You have the option to conclude that employer has become unworthy of being employed with any more and terminate the relationship. You must keep your next employer/HR in confidence and appraise them. Everybody knows the trends in the industry.