Thanks to everyone for your help and suggestions. Seems like it's a hit and miss thing for me right now. I went outside and walked away from my router and tried to access the internet and found I was offline, which is what I want. Then I walked even further away and I was back online again. Bizarre. Even searching the net for solutions have proved futile.
It's all very bizarre assuming you've done all the right things. You have developer options on and found "Mobile data always active" set to off. Do you leave developer options on all the time? I wonder.
You've turned off all the background data settings in all the apps you don't want doing that.
This may be for dual-SIM but you have "Mobile data only apps" set to off.
Play store certainly should respect the setting to not update on mobile data.
Edit: testing going outside like that is a nice repeatable test. That would help in finding the culprit.
@darlicious , yes my limiter will limit my data usage. I have it set to give me a warning at 200mb. But today, i used up to 180mb without knowing it. I never use mobile data unless it's an emergency and that would only happen if I have car issues and I'm stranded in the middle of nowhere.
@z10user4 , leaving Developer's options on or off I get the same results. I just don't think there's one constant causing this to happen. Results appear to be random at best. I guess I just need to be more wary everytime I go out.
You need to set your data warning much lower at say 50mb and your data limiter at say 100mb. Then you get the warning that something is up when its only used 20% of your data. If for some reason you don't notice the warning and your data continues to be used it will then just stop at 100mb or 40% of your data. You could set these much lower at 5mb and 10mb to truely conserve and test when your mobile data is being enabled on its own and there is data usage.
@mobileguy did you set your Google Play store to update via Wifi only?
At Play Store, Under General, tap Auto-update apps, enable Auto-update apps over Wi-Fi only
Also, did you check Mobile Data Usage? It might be able to show you which app stole your data.
@softech , I will look into that option. Maybe I don't have that set as a default.
After experimenting a bit more last night, I found something that appears to work. However, I can't say if it's a permanent solution. I find that when I'm at home and still connected to Wifi, if I disconnect Wifi before I got out, I'm offline no matter where I go afterwards. My internet connection never got reconnected automatically for the hour that I was out. Again, not sure if that will work everytime but it's something I'll be keeping an eye one.