50 days when I received email for my promotion but HR team is not providing me with any formal letter for my promotion

Hello Everyone, I got promoted in my organisation after submitting my resignation. Its been more than 50 days when I received email for my promotion but HR team is not providing me with any formal letter for my promotion. They are delaying things and giving silly reasons like it is due to some technical issue or waiting for approvals and other stuffs. I want to know if there is any policy or rule which could help me in getting my promotion letter. My last working day is 12th August. My organisation is top among top IT service provider. Looking forward for your response. Many thanks in advance.
Mayank Pant

Hi Mayank,
Surprise that your present employer had promoted you in-spite of you resigning from your post. You have mentioned that they have emailed you about your promotion. Forward that email to your personal id and take a copy of the same, if needed. This might also be a retaining strategy which they would have tried.

The promotion was probably planned and the HRMS would have released it on original schedule.
Or as Mahesh says, it may be a retention strategy.
In either case, why will they give it to you ? You are not staying, so why will they actually promote you.
There is no,legal basis to demand the letter, so forget it and move on.

Mr. Mayank,
Promotion is for working employees, not for birds ready to migrate. Forget it.