My iphone screen is almost black?

A couple weeks ago, I dropped my iPhone and the screen turned completely black, after a couple minutes it turned back on and everything was fine. My friend then dropped it again and it turned black once more. I thought it would turn back on again but it just wouldn't. The actual phone was fine, i could check my notifications using Siri, I could unlock the phone by remembering where the unlock bar was it was just the screen. So i went to apple and they told me it was probably something near the LED sensor or something, and they tried fixing it but it did not work.

A couple days ago I realized that it was never black, if I went in the (bright) sunlight I could see the screen (in very low brightness, possibly twice lower than the lowest brightness available)! I tried going in settings and changing the brightness, lower or higher, nothing would change but everything else works. How do I heighten the brightness?

I think it is actually bad. You must repaired it.

If it is at its maximum your best option is to restore it. If that doesn't work it has been damaged and needs to be replaced.

If only the brightness thing isn't working there then you may make a factory restore on the device, that would probably just turn OFF all those manual setting done on your device since you got it. This would surely change the brightness to the previous one, as far as it's my concern.