I can’t setup voicemail on my new iPhone 8
I’ve been into the att store and was told it was an Apple issue
Voicemail service is provided by your cellular wireless provider. In this case AT&T. I am surprised that the AT&T Store representative did not get this resolved for you. Apple cannot "fix" this.
However, if you are referring to Visual Voicemail, the following articles may prove helpful:
- Set up Visual Voicemail on your iPhone - Apple Support
- iPhone Voicemail Won't Play? Here's How to Fix That - OSXDaily