Hi,
Did you have any communication with the HR department in this period of 3 months? It would not be a big issue, if they just forgot to process the reliving activities. They can process it & relieve you from the company quickly (2-3 days). Then you may want to extend your services for that small period.
Any way, it is mandatory that the employer responds to the resignation with acceptance or rejection, with valid & clear reason. This letter generally also states the last working date. If you have received any such communication from HR, then the notice period may be calculated starting "after the date of acceptance" & not "after the date of resignation".
If this is not done by the employer, & if they also do not respond to the letter format suggested by Gia in above post; then you are free to stop work after the notice period, as mentioned in the contract. If you want to do this, then please write a letter to HR stating that you did not receive any rejection response in the deemed period, hence the resignation is considered accepted & as per the contract, you would like to discontinue your services after notice period. Then you can still obtain relieving letter & F&F settlement later.
Regards,
Amod.