My employer is scaring me of courts notice. please advise

Greeting Sir, In February 2020 i joined an internship in company my internship was of 6 months WITH STIPEND OF 5000 , but after 2 months of joining there was a lockdown and they said thry have no work so i had to sit for 6 months and then again in December they called for to continue my internship for 4 more months to complete it and also increased my salary/stipend by Rs 5,000 MAKING 10000 PER MONTH. when my internship got completed on march 31, 2021. he gave me confirmation letter AS comfirm EMPLOYEE . but when i asked for Internship completion certificate he said that your internship is incomplete as we increased your salary in between of it. if you want it work for 4 more months on Rs 5000 /month then i will give the certificate. but working hours is worst and learning is zero i resigned on 5th july 2021, and sent all the company's perperty on10th july 2021. which i had since it was Work form home i had companies computer and other things. after resignation he said that i have to pay 3 months salary or serve the notice period of 3 months. which i signed during comfirmation of my job on 31st march 2021, as he is saying that he will take legal action and send me the court notice for not serving the notice period or paying the money. i'm scared that what if he does sends the notice period.As i will not be benefitted even after serving th notice period, according to him my internship is not completed and i have just got the confirmation letter on april 2021 i get nothing from his side, i have wasted 1.5 years and did not get anything from company. so i decided to resign and not serve notice period i will not be benefitted by serving the 3 month long notice period. please advice me will go to jail or he is just scaring me, I DID NOT EVER SIGNED ANY CONTRACT OR BOND WITH COMPANY . I JUST SIGNED THE CONFIRMATION LETTER ON COMPANY LETTER HEADER, WHICH IN ONE ITS CLAUSE SAYS THAT I WILL HAVE TO SERVE THE NOTICE PERIOD OR PAY 3 MONTHS SALARY.