Hey there divine147,
Thanks for reaching out to Apple Support Communities. It sounds like you’re having some issues allowing certain apps to use cellular data on your iPhone. We understand how that could cause some issues with accessing the app when you’re not on Wi-Fi and we’ll be happy to help.
If the option is turning off by itself, start by checking if Low Data Mode is enabled:
Use Low Data Mode on iPhone, iPad, and iPod touch
Then check for any updates to iOS:
Update your iPhone, iPad, or iPod touch
Then force close Settings and restart your iPhone:
How to force an app to close on your iPhone, iPad, or iPod touch
Restart your iPhone
See if cellular data stays on for these apps after this.
If the issue continues, delete Instagram, restart your iPhone, then install the app and try again.
We hope this helps.
Take care.