We are seeing frequent reports here, like yours, where owners of very devices with very old versions of iOS are having this issue. The only explanation that we can currently offer is that Apple have changed something in their back-end servers that now does not recognise these very old (i.e., now unsupported) devices.
Likewise, many (if not most) Apps in the Apple App Store have ceased support and no longer work with very old versions of iOS. This is the unfortunate price we pay for progress - and as much as we may like them to do so, our devices don’t last forever. We are perhaps fortunate in that a high proportion of Apple hardware outlasts the underlying software - a luxury that is rarely seen from other hardware manufacturers.
You have two options to pursue:
1) Raise a support request directly with the Apple Support team - you’ll find the link to Contact Support at top-right of this page.
2) It is perhaps time to consider replacement of your device with a newer model - which will provide you with significantly improved performance, wide compatibility with current Apps, and an upgradable Operating System for many more years.
I hope this is helpful to you.