You can file a complaint to labour commissioner in the  said aspect

File RTI application as to why you have not been relieved although 5 months have passed since transfer orders were issued 

file application before SAT against delay in relieving you 

Drop a mail to the receiving department that to request the serving department to relieve you as early as possible , better is to visit the place and talk to the higher ups there and bring a hard copy with you and get the same received to the serving department and wait for 15 days then on 16th day file a writ before the Hon'ble High Court for the relief and you will get the same, but better is to file the writ after 23rd May 2019 as they may say that the code of conduct has been implemented and they will relieve you after that so wait but complete the formality of letter right now.

Approach concern authority or you can file an RTI application. 

Hello, 

What is the reason they are giving for not relieving you? 

Also, have you given any representation to them? 

Also. what does the transfer order mentions? Does it mention that you should be relieved immediately ? 

Regards 

Through a representation to be moved before the Competent Authority, request for an early relieving. 

If no heed is paid to your representation, approach CAT> 

Inform the higher authority. Moreover if date of joining is given in order than you should have joined it. Now fresh order will pass otherwise may consider for disciplinary action.

Have you made a written representation to the top management of the organisation in this regard and have requested for an early relieving order?

If not do it immediately.

If you dont get any reply or response to your application/representation then you may plan to approach Sate administrative Tribunal with your grievances for relief and remedy  

Dear Sir,

If you are not receiving relieving letter as your ex-boss states, you may take legal action based on your exit mail.