Collect Debt from Previous Flat Mate (docs & proofs available)

Hello, I am resident of Lajpat Nagar, New Delhi. Long story short - My previous flat mates owed me money since July 2015. I havnt pushed very hard because he was switching jobs and cities. Now that he is settled back in Delhi I approached him demanding the dues. He now denies blankly that he ever owed anything. More Info - I have all the bills i paid for him well documented in a Cost Sharing App called 'Splitwise'. Yes all our expenses were well calculated. He is on the app as well. In September last year i sent him a mail asking me to acknowledge that he owes me money. I added a few other clauses and asked him to acknowledge. After settling on a few charges on the app - we settled for a final amount which he promised he will pay. All this is in writing either through email or whatsapp. He cited low income and family pressures that unabled him to pay but assured me that he will pay once his next set of cheques clear out. All this is in writing. But now that he is in Delhi he has stopped picking up my calls. Over email he expressed how he never owes me any money now. I need to know is there anything that i can do legally. Anything that can make him pay the money. I assure you that he is financially capable of paying me now. As i mentioned again and again - every single penny is accounted for and logged well in the common cost sharing app and he has agreed to pay me the amount in writing (over email). Any help would be much appreciated.