Not got experience letter and Relieving letter from the previous employer

Hi, I am Mani. Below are the concerns that I had, I got resigned in 12-July-2018 and got relieved in 22-October-2018. I served notice period of 3 months and 10-days. But, at the day of relieving my HR was said, that they cannot provide relieving letter and experience letter to me. I asked for the reason, that they were telling I signed one self declaration agreement. In that one point is there that is I wish to serve for 3-years like that. I worked here over 2-years, but they refuse to gice experience and relieving letter. I told them, I am facing some partiality and internal politics played on me and I cannot able to work on this pressure is building more. They are not concerned about that, so I put a resignation and completed all work before I am leaving from the previous employment. I got best performer award everything, but faced some misunderstanding with my previous company manager. So I can't able to work with pressure work and by manager. I referred employment for my friend in my previous company, he worked for 9-months only and got both relieving and experience letter after 30 days of resignation. After I got out, I spoke to my manger and HR, but still they are not willing to provide me a relieving letter and experience letter. But HR sent one mail, that I got relieved in the date of 22-october-2018. But I was in need of experience and relieving letter of my current new employment or job. Thanks, Mani