Daddy wants a quiet life but has a 9yo daughter.  These two things don't go together.  You are going to have to spend some time in the Disengagement forum and bone up on that skill.  You can't care more then the parents but you do have to protect yourself from getting hurt from the daughter.  

You don't say how old you are but I will tell you that there are more men out there and the odds are in your favor you find another one to love that doesn't have this baggage.  

While I may not agree with a 9 yo having a social media account, if it is an account basically monitored/hosted by her mother then I honestly think you overstepped by reporting it to IG.  If her father wanted to escalate conflict with his child/EX then that was his option to do so.  You took parenting choices away from the parents. 

And.. I can see that people will say.. "well rules are rules..." but honestly, if it's not impacting ME personally and is not causing harm to a third party then I am not going to step in and be the internet police.

there is a difference between fudging the DOB to open an account vs someone setting up a "myspace" page and stating publicly that they are much older than they are for the purposes of attracting the attention of older boys.. (as my OSD did).  As long as the settings were set appropriately for her age (private) and you didn't see her angling for dates.. then I think you should have left this to the parents to work out between them. 

I think your heart was in the right place, but you cannot worry more than the parents and your morals and rules may not be the same ones they choose for their child.  You have to defer to their judgement unless it is a truly risky behavior.. like letting the 9 yo do drugs...etc.

It sounds like he has never seen a grown woman care properly for a child.  You did nothing wrong in my opinion.  I might have kept it a secret about the reporting of it though.  Now you know.   Little girls do not belong on social media and there are plenty of stories out there about pedophiles going after them.  That her parents don't know this or worse, don't care is disgusting the day and age.  

When he comes back , don't grovel, don't be a doormat.  Be strong and be a woman worth respecting.  You only had the best interest of the child in mind and acted accordingly.  Then explain that from now on what you will and won't do for SD. If he doesn't like it or wants you to do his job, then he has to give you permission to act in a parenting role with her and back you up.  He can't have it both ways, it doesn't work.  Either you parent as a team or he parents on his own.  Then hold him to it.  

This fight is a growing pain of blending a family.  Hopefully it will be a lesson learned and you can move forward from here with a better understanding of each other and the roles you play in your home.  

About 2 years ago, I was awakened by the sound of my then 10 year old stepdaughters phone going off. When I picked up the phone to try to figure out how to turn it off, I noticed on the screen that she had received a message in some type of chat app from a 37 year old man in another state (the only things about him were name/a/s/l). The message read, "Good morning, baby." That was all I saw since it was just a pop-up notification and not the real app. Plus, I am not tech savvy. I can barely use my own smartphone. 

When I informed my DH about it, he didn't see a reason to question SD10 about it or to check her phone.The BM and my DH didn't even have the password to her phone. Two years later and after this incident, they still don't have the PW or check how she uses the phone.

That's when I decided if the bioparents don't care that a potential predator is contacting their daughter on an app she's not even old or mature enough to have, neither do I. I know it sounds harsh, but that's the reality. 

You really cannot care more than the parents. It will make you feel and look crazy and controlling when you aren't.

You can't fix someone else's ability to give a damn.