Employer not giving experience certificate and reliving letter after serving 2 months notice period

I worked in a Private Ltd company for 3.5 years and after getting offer from an MNC I sent resignation letter (in mail) to the HR & Dept head. I have given hard copy of resignation letter also to my dept head. After the discussion with HR, she told me salary buy off for notice period is not acceptable and need to serve the complete notice period. ( 2 months as per appointment letter) So I served the complete notice period of 2 months. But the HR is not processing the relieving documents and she is saying that the CEO of the company not accepted my resignation.( Verbally only, i have not received any mail on the rejection from HR/CEO) Since i need to join the new company i can't work there till they give me the reliving. So i left the company on the last day of notice period. On the last working day i have sent mail to HR & dept head saying that today is my last working day as per notice period and issue the relieving documents. After waiting for a week i joined new company. I informed the new HR that i resigned from old company after serving notice period & didn't get the reliving letter yet , so can't submit the reliving letter on the joining date. He agreed to join there,but need to submit the relieving letter with in 2 weeks after joining. Finally i joined there, otherwise I will loose the offer. But now 2 weeks is almost over and the previous HR is still not processing the relieving as the company CEO not accepted the resignation. Also they have not given me the last month salary stating that i resigned from there with out management aproval. 1. Is there any issue as i joined new company? My previous employer does not processed my reliving. But i served the complete notice period. 2. Whether i need the CEO's acceptance to resign? As per appointment letter only mentioned to serve 2 months notice period. 3.What i can say to my new company on this as they are expecting me to submit the relieving letter in next 2 days. 4.Whether the old employer can legally take action against me & new employer ,as i joined new company without getting reliving documents from old employer. What are the consequences? 5. What can i do to get the relieving documents & experience certificate. Kindly advise on above questions.