you can not do anything.
you can only file query with excise department every 3 months for the number plate availability with receipts of registration and payment made for number plates, for which you are still waiting. Legally you can not do anything, there will be on liner reply number plates of year xx series xx are not received from the manufacturer please wait.
the number plate scam has plenty of stake holders. the pair of tin plates which costs under Rs. 300 is charged twice sometimes 5 times heavy from customer while there is huge financial kick backs involved for obtaining number plate fabrication contracts.
You may try to engage a tout outside excise office pay some extra speed money to get number plates in hand.