First, you may send a legal notice for recovery of money to the ex tenant asking him to pay the rent as well as other outstanding dues. A legal notice is sent as a warning to the receiver regarding certain grievances which are not properly taken care of by the receiver, although the receiver has been given enough opportunity by the sender to resolve the problem. The legal notice acts as a warning and on no response you can take the matter before the Court.
If he does not pay within the next 15 days after the service of notice then you may file a suit for recovery of money against him.
You can file a civil suit against the person under Order 37 of the Code of Civil Procedure, 1908. Order 37 is a power given to the person who wants to recover his money. Once the suit is filed and summoned, the defendant will be given 10 days to defend the suit. After that if it is proved by that the other person has taken money and is not paying it despite several reminders and service of legal notice, then defendant has to pay money and punishment can be served to the defendant.
Reference: Code of Civil Procedure, 1908