Storage issues

For sometime my iPhone 6plus has been acting up lately , whenever I delete pictures and delete apps to Malena some space for other stuff

system immediately jumps in to fill the gap in the free storage I got in a mere seconds

yesterday I tried to clear my storage and I had 700 mb free

so I went to AppStore to download back Instagram

and it said it doesn’t have space

I checked storage

it’s was 15.9 full out 16 GB

and system and settings took up about 14.9 GB

i am so sick of this

my phone won’t let me even delete an unwanted update

why do we get unnecessary updates for each half a gigabyte

it’s not even that useful in the long run

please help me find a way to get this problem out of my phone