Dear [Login to view],
Further to Ankita's suggestion, I'd like to add, that keep in incessant transcribe with the Human Resources. An email follow-up is a great idea, alongside why don't you try sending out the resignation letter with a reminder to the Head Office through a Registered Post with AD. It saves a lods of stress as an acknowledgement will be received to you. If you haven't then a second REMINDER along with the RPAD copy attached to it can be produced to the HR for necessary action.
Take a crack at this procedure you are sure to get an outcome of the same. We wish you to update us @ CiteHR, as there are many here in the forum to benefit the endeavour.