Friend won’t return my money

I lent 12k to friend of mine and he’s simply not returning it. He borrowed this money from me back in October and since then he has been making some or the other excuses. I believed the excuses as we’ve been dealing in money for well over a year and a half. I’ve lent him even 40-50k at times and he never delayed any payments for more than a week. He made a very sturdy promise of returning it on 10th Jan, but his phone is switched off since then. What action can I take against him? TL;DR: Friend borrowed 12k and won’t return it. His phone is switched off since the last 3 days.