Help! Almost Done My No Contact!!

Hi Everyone! My boyfriend of 3 years broke up with me recently, because he was bored with our relationship and told me that I do not challenge him enough. (He is 27 years old and I am 25 years old, so this was a very serious relationship).
Of course I begged him to come back after he broke up with me, but he told me to stop contacting him. He blocked me on Facebook and possibly my number (iPhone makes it hard to tell if you have been blocked or not).
I am now on day 27 of no contact, and I have really been focusing on myself and making positive changes, even though I do want to get him back.
When my no contact period is done, do you think I should mail him a letter telling him that I accepted the breakup. And say that I also have had a lot of exciting things happen and would like to tell him about it when he’s ready?
I feel like a letter would be a little more effective, instead of texting since I don’t know if he blocked my number. Let me know what you think! Thanks so much!