Legal notice by employer for not serving notice period

My husband left his job immediately without serving notice period of 30days the company has sent him legal notice asking to give the salary back in 15days orelse he'll have to pay them salary + 3lacs compensation. He was on probation period basically joined in Dec 2020 end and they have 6 months probation, in appointment letter they had 15 days notice in probation which company change in Feb 2021 to 30days. Reasoning for leaving was also that while they hired him was informed 9hours duty with one weekly off, wherein daily his shift use to extend by minimum 1.5hrs extra without pay (No OT) plus once on duty his 2 wheeler got stolen from station as it took him 1am to reach back home from his job we live in Naigaon suburbs of mumbai. So they're into medical profession, he is lab technician, the company's rule is anyhow they should complete 450 to 500 sample testing on daily basis then leave from duty,as they promise customers reports in 24hrs. Fortunately he got another chance with fix shift and off's even it's lesser pay, important was peace of mind. On the previous job he was getting too stressed out impacting family life too, hence when he got his salary he left same day completing his shift and post which he send immediate resignation on mail Now the demand that company is doing asking him to serve notice or pay compensation is worrying us and unfortunately he can't join again as he ia started with new company already. Any suggestions on this query