purchase of second hand vehicle

i have purchased a second hand vehicle from a car dealer for Rs 420000 in may 2017. At the time of purchasing i was told that cost incurred for transfer of ownership will be borne by the dealer. after around one year change of ownership is completed and my RC is with dealer. now the dealer is saying total cost incurred during ownership transfer is 22000 and at the time of selling the vehicle they included 15000 for ownership transfer and i need to pay Rs 7000 more to get my RC. if do not pay 7000 rs to them , they wont give me my RC. i do not want to pay this money since i have already faced a delay of 1 year for ownership change and i do want to get extorted. what legal action can i take.