I can't change the volume on my iphone?

When I press the volume buttons on the side the volume icon shows up but nothing happens. Then when I try to change the volume from the task panel the grey slider knob is gone. I shut my phone off and it's still happening. What can I do? And no, the silent switch on the side is off.

Goto

settings>general>accessibility>assisti… Touch>toggle it to on

now an icon will occur on your screen

touch that press device and volume up

hope it will work

I tried that but it doesn't work… I also, when I use qqmusic the volume icon doesn't even show up