Lumia 640 Win10 upgrade issues

My Lumia 640 with AT&T won't seem to upgrade to Windows 10. I have tried upgrade advisor, Insider preview, even the developers preview apps, all with no luck. Using The Insider preview app I get an error message every time saying to "check my network connection and to date/time settings and try again" I'm not sure what to make of that I have checked my date/time settings and they are set to automatically update and my network connection is fine although I do not have a data plan I I'm connected through AT&T with talk and text using Wi-Fi. I have attached a photo of the error message. Everywhere I look it says my phone is eligible for the update but I have yet to be successful. If anyone can help me out with this I'd appreciate it very much. Thanks

Source: Lumia 640 Win10 upgrade issues