@Jade1-
Try logging in on WiFi which will prove if it's network related or not.
If the app won't let you in on WiFi you'll need to speak to Instagram for help.
I have no affiliation whatsoever with O2 or any subsidiary companies. Comments posted are entirely of my own opinion.
This is not Customer Service so we are unable to help with account specific issues.Currently using:
Pixel 7a (O2 & Lyca), One Plus 6 (Sfr), iPhone 12 Pro Max (Vodafone)