Money Owed By Car Aggregator, Withheld Car For Security, Can It Be Sold .

We have a car service business. We did car service for an aggregator and they owe us some few lakh rupees. The aggregator is not responding, so we withheld few cars after service as security. The aggregator is still not responding after we even sent a notice through a lawyer. Since the aggregator closed the office the notice came back. It has been now almost a year and the case is not able to make any progress. Is it possible for us to sell the car in order to get back our money or do we need to wait for legal proceedings? Since the aggregator doesn't owe these car not sure if we can just sell those cars to get back our money. Please advice