My phone keeps on saying 'Storage almost full' and i have 0 bytes available even i've deleted more than 2000 photos and 20 apps . What should i do ?

I had problems with my phone memory storage. When i was about to take a picture, it keeps saying not enough storage.

So i opened my usage information and..

it says i have 0 bytes available. Then i deleted more than 2000 picture & more than 20 apps.

IT'S STILL THE SAME.

still 0 bytes available. i do hard reset after it. and i look to the usage information again. it said 1,4gb free.

A minute later, a notification came to me : Storage almost full, then i go to the usage information.

It's back to 0 bytes available.

after that i keep on deleting apps, and it has no effect at all. i've deleted more photos & videos, but nothing's change.

I've read the tips about changing my phone date into past months, i did, and i restart my phone after that.

It says 900mb available, i pressed back, and press usage again, It says 0 bytes available.

I can't take any pictures because of this.

Also after that i tried to delete my path, instagram, twitter and it still remains the same. Now i can't even download it back.

About recently deleted photos, that features only works on ios8 right ?

I haven't updated my ios for now, still on ios7.

How could i updated my ios if i don't have enough storage for it. i can't even download an app / taking picture !

But the strange things is, sometimes this full storage case happens most when my phone battery is low. And back like normal when i charged it to more than 80%, but this time it doesn't matter how's my battery condition, it's still 0 bytes available all the time.

When i checked it on my computer, it says that i have more than 500mb free, i still can even add more musics using my computer.

i could capture a screen, but not taking pictures / videos.

Last night i slept with 600mb available on my phone, and when i wake up, it says 0bytes available. It's so stressful.

Anyone have a same case with me ? Please help me how to get rid of this issue. Thankyou.