I changed my Apple ID but my iTunes hasn't updated so I can't access it...do I need to reset all devices to factory settings? or how else do I get the iTunes to link to Apple ID?

Question

I updated my Apple ID primary email address without having switched off 'Find my....' on all devices. A 2 hour very helpful call with Apple Support solved ny Apple ID and ICloud. Later, I tried to update apps but my iTunes account is still on the old ID and I can't access that email/password anymore. I can't get a support appointment for 48 hours but need to update travel apps soon!
Do I need to reset to factory settings on all devices (5!) and start again...or how else can i get iTunes to link to my Apple ID now?
Any help appreciated!

Answer 1

Thanks, David. But that was the first thing I tried. For some reason, when I try to change my Apple ID back to my old email address, I get the message that that Apple ID is already in use and so I cannot use it! I have tried requesting a password reset using my old Apple ID email, but I've waited and waited and nothing has come to my old email address. This is sooooooo frustrating!