Legal Notice from employer for absconding with 1 month of joining

Hello Sir, I just received a legal notice from a company I joined on 26th June. There are 13 points they have mentioned in the document and asking for a penalty of INR 8 lac + 10,000 (advocate's fee). I resigned on 19 Jul and as per my offer letter, notice period was 45 days but Client asked to serve 90 days (which I had told them about my terms as per appointment letter) so last working day was supposed to be 1st Sep. Then I had applied for 5 days leave and requested for extension and the new last working date got changed to 7th Sep. As per their salary processing policy, I have to submit the monthly time sheet with all the necessary details such as 'Present, Leave, Public Holiday, Compensatory Off, etc' then the salary will be processed. If submitted on the 31st of the current month then the 7th of next month salary will be credited, if 1st then 9th, if 2nd then 11th and so on. I shared the time sheet for July month on 31st July but the company had reverted to the same email on 1st Aug asking for details about a Public Holiday at the Client side. I could not reply to that email and directly on 7th July they called and asked to forward the time sheet again. I sent that on 7th itself and received a salary on 9th Aug 2023 for the month of July. I submitted back the office asset to the Client and dropped an email on 10th Aug that I will not be serving the complete notice period due to the policies and unprofessional behavior of the parent company. I am not sure with this experience, I will get my Full and Final settlement amount properly on time or not. They called multiple times threatening legal proceedings against me but I do not want to continue with them at all. What should I do next?