Notice period wavie off

Hello, I am suffering from Back Pain for more than 3 weeks and I have all medical records and my doctor as advised me to take rest for further days and avoid work. But I was in notice period and I am not interested to continue work in organization and serve rest of the notice period. So I requested management for Buyout due to my health condition at first they agreed and sent me the calculation that I have to pay for rest of the notice period but then they stopped me at the time of payment for buyout. And advising me to take rest for few days/weeks and come back again and serve notice period. They rejected my Buyout saying (Notice period buyout is Company's sole discretion to accept or reject such notice period buyout option with or without assigning reason) which is same mentioned in joining letter. My question is if these was the case why they did not rejected my buyout at first stage , but instead they gave me the last working date with payment details which I was ready to pay. And last question is does company can reject Notice Period buyout when an employee have health issues.