i had/have this problem too! I really don't want to reset my phone with DFU and stuff because i don't want iOS 10 either but i still wanted to have iOS 9.3.3. So i tried instead to just hold down the power button for like 20s or more and then the charging icon showed on screen until i released the button. So then i plugged my phone into charging in the wall and held down the power button again for like 20s and now i think it has started charging... idk if my phone did this just because of jailbreak but you can try atleast