Sir,
Please send a legal notice asking for the same and in case of failure he is liable to pay compensation for the harassment caused.
If its builder flat then a case under Consumer Protection Act can be file seeking compensation.
You can also file a police complaint for playing fraud and selling you the property under the pretext of fraud and now he is not giving the parking keys because his intention was never to give the car parking.
Last but not the least, it is a case of breach of contract on the part of the builder as well, if the same were mentioned as the terms of the contract when the flat was sold.
Regards
Kapil Chandna Adv
9899011450