Thanks a lot. Turns out I was subconsciously doing this kind of escalation. I called up a co-worker (who is now a manager in that company). He listened to my r

Thanks a lot. Turns out I was subconsciously doing this kind of escalation. I called up a co-worker (who is now a manager in that company). He listened to my request in a friendly way and was willing to write a letter for me. However, to verify the contents of that letter, he contacted my ex-manager. That put social pressure on him and he replied with the letter. Gradual (but polite) escalation worked wonders.