Full and Final Salary not paid by the previous employer

I resigned from Global Upside, Noida on 15-05-2019 on medical ground. I have been diagnosed with kidney disease, high blood pressure and electrolytes imbalance and hospitalized for the first time on 2nd April, 2019. Subsequently, I was hospitalised 3 more times as my condition worsened periodically. For one and half month I kept updating the management and HR about my health status. The senior manager - HR asked for my medical reports, which sent via email on 19th April. Later, after my resignation, the Senior Manager-HR called me on 20th May, and asked to return the laptop via FedEx and mentioned that after receiving the laptop, they will initiate my due salary and issue my experience letter. I sent the laptop via FedEx on 24th May and confirmed via email. After sending back the laptop, I have done several followups, but received no response from Global Upside. Before resignation, I worked for 4 days and then applied for 8 days earned leaves. So, there are 11 days salary due. I did not receive this amount later. My question is can they hold because I could not serve their 45 days notice period? I could not do so due to my health. Awaiting reply. Thanks.