Why won't ZTE Blade Q mini download an app even though I have sufficient space?

I have moderate use of phone from March 2014. I have installed max 4 apps. The Barclays app now needs an upgrade. Q Mini will not allow. Not enough space. Added 30GB SD card. No improvement. Deleted app and tried to re-install. Q Mini refused. Same reason. Effectively then this 3g Phone is at the end of its life.No apps can be added.

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