This is [you] and I have worked for [x years] with the [department] of [company] as a [position] for the period of [from date] until the effectively of my resignation which was [to date].
Despite the fact that I have completed everything that needs and are expected to be settled from my end until now, I still do not have my experience certificate and my relieving letter which will be important for the company that I will be working with. One month has already passed since I resigned but my experience letter is still pending. I am positive that you will help me in this matter and I wish you can reply the fastest that you can.
Thank you and Regards,