I've received legal notice from my previous employer

Hello, I need some consultation about following. Scenario: I was working with Mumbai based startup from 04/12/2017 to 20/04/2018. I was working remotely. As per my contract, I had to serve the notice period 1 month before releasing. I had resigned & served properly a month of notice period. The reason for leaving the company was unorganized work & got better opportunity. Now while working with the company we had some commit to finish some work till 31st March(which is normal when you are working). Since, I had decided to move out & the work was not completed because priority changes in work & other dependent factors. The company owner didn't sent me the acceptance of resignation on email & neither termination letter(Company owner was speaking nicely when I was working) & I thought things are fine. Now I've moved to other country considering my employment is terminated & I've served proper notice period. 1. The company has not processed my salary & April month(for 20 days), when asked on email they says fnf is not done. Once it is done they will process. 2. For fnf they are considering I should finish the pending work, even though now I'm working with some other company. 3. More to that, they have sent me the legal notice about the work pending & company's loss. There was nobody to handover so I had not done the handover & things were fine when I was leaving so I said I'll do it later as well. 4. They sent me some emails about pending work after I left the company but as I was busy with settling down at new place & new work, I did not replied them. As per our mutual discussion I was yes to work even I left the company for few pending things but I really don't work on that stuff. My questions are below: 1. Do I need to reply to their legal notice? If yes, how should I do that? 2. I was thinking of giving handover & work on their pending things even I've left, but should I do that? 3. Is there any base to this legal notice, since I've served the notice period properly? Note: I'm outside of India now! Thanks in advance!