I am an international masters student in Germany. I started working in a company in August last year as a work student, but after 3 weeks of joining the company I went back to my home country as it was my semester break. This is something I had already communicated in the interview. I kept on working after coming back at the start of October until the end of December when I resigned because I found a better company which had better work company and their project was much more appealing. My previous company had 15 employees but my new company has 2000+ employees at least.
What I did wrong is that I lied to my ex-employer that I am leaving because I cannot manage my studies but still I finished my notice period of one month. Now it's been more than 3.5 months and I've been asking him to give me a letter stating that I worked in his company for those months. He keeps on saying that he would do that when he has time. He also somehow found out about my job and he sent me an email stating that he was furious with what I did. I lied only because I knew he would persuade me to stay and it's difficult for me to say no to people. What should I do now?