if the key doesn't fit the lock or start the car then you need to be going back round and finding out why not

there may be a car mising from your driveway i someone else has got the key and knows where you live, haven't you seen gone in 60 seconds

but seriuosly, who's got your ky and who's key have you got then?

speak to the guy who sold you the car
manager next until you get it sorted

just don't leave the car there wihtout some sort of transport back again as you'll be without a car until they fix it