Need advice

My ex middle son had a bday on September 1st, and that's why i guess she tried to reach me on September 2nd 4 times on calls. I m in no contact from last 19 days.i have spent 3 years of bday with him and i couldn't this year due to breakup. I don't understand what should i do? Should i call on his phone to wish him and let him know that i didn't abandoned them. I don't want kids to feel like i just packed my bags and left. Btw my ex gf new bf already met them next day i officially said my final bye to them. They were crying. But their mom make them meet new bf 7 days after break up. New guy already living in their house now. Any advice would be helpful. Thanks