If you look on the previous page, the Community Moderator has replied.
—————————
“As already stated clearly above, there is nothing wrong with your phone and nothing you do with it will resolve the problem. You just have to wait for MS to sort out the problem from their end.
This issue comes up on regular basis, as you have already observed - thank you for making the effort, unlike the dozens of others who blindly post new threads on the same page already full with the same question asked over and over again. Usually
it is resolved within 48 hours or so.
You might want to consider upgrading the 640XL (there is no Lumia 645) to Windows 10 Mobile, since support for WP 8.1 ended in July 2017 and the store will be supported for around 12 months after that.
https://support.microsoft.com/en-us/help/4036480/windows-phone-8-1-end-of-support-faq
What does end of support mean for customers?
End of support means there will be no more product or security updates. This is in-line with our Support
Lifecycle policy.
Even after end of support, automatic or manual creation of new device backups for setting and some applications will continue for 3 months, ending October 11, 2017.Other services including photo uploads, restoring a device from an
existing device backup and the Store will continue to work for at least another 12 months from end of support, after which time, services will start to be discontinued.”