It's on IOS btw

I am having the same trouble with dethroning the dark prince on Android.

I have a quest called 'Time to Win' where you need 20 Win streak battles in the arena before the streak timer runs out that has been stuck at 13/20 for about 2 months now. Really annoying. 

Have you actually got to a 20 win streak in the arena lol?

If you haven't then it will show your previous best, which in this case would be 13/20.

yea got to 15 twice since then. I just wish i could drop it from the quest log so I didn't have to keep looking at it haha

Same here, that dam quest is the toughest one lol.  Especially when you are leveled up

^^^^ Exactly dude, I kind of refuse to spend actual money on this game but I'm up in the lvl 60-70 range getting blasted by people that are 3x as strong as me. 

Yep, I'm at lvl 101 and haven't spent a dime... which is probably why I am still working towards getting my first Epic haha

clear the data on your device, go to app manager and find Knights and Dragons, hit clear data, it will NOT erase or lose your account, it is bound to the device itself, then open KnD and let it load your knight back up. that is for Android, i have no idea how it is on iOS lol but im sure you get the idea

You can do this, if this does not work, try an uninstall/reinstall.

For either way make sure you are using WiFi or have a good data plan, when you reload the game it kills your data if using it. I have used both ways to clear small glitches that appeared in the game in the past.