IPhone can't connect to iTunes?

I still have iOS 9 on my iPhone SE, but everytime I tried downloading an app it said can't connect to iTunes, I tried to sign out and sign back in but I couldn t. Now everytime I try to sign back in it says can't connect to iTunes. I can still go on other apps like Twitter, so I know it's not my Wi-Fi, I also just changed my payment details in case that was the problem. I can't sign in to my iTunes even on my laptop. Nothing seems to be working. Any ideas?

The outdated ios prob the cause of some, i would power off the iphone when battery above 60% holding the homebutton in connect the phone to pc /itunes, will be in recovery mode and restore or update, will download via itunes latest ios and install… As for the inability sign into itunes… Mine keeps saying failed / unknown error… Yet i'm signed in, unable authorise this pc but authorised, yet another of Apple series of issues, i have a 5s / 6 / 6s and SE of my own and repair them so now just roll with it lol just to clarify, you do not need be signed in itunes via pc to use recovery and on setting up use your id and choose from latest back up… Make sure either leave in usb port or switch to charger better after updated and syncing back

Follow this support link from the apple website
https://support.apple.com/...b/HT201400

are you sure you are signing in with the correct apple id and password?