The power jack of the keyboard is broken. You have to disassemble the Keyboard and look if the connection from the Mainboard to the Power jack is lost. Make pictures when it's open.
1: did you try to charge the keyboard individually? 2: does the dock and the phone even charging when they are connected with the keyboard? if the second is right than either the battery is broken or there is no battery in the keyboard.
If you remove the battery and test with a multimeter how much voltage is in the battery and how much voltage is on the board where the battery was plugged in than you can say if the board is broken or the battery. How much voltage it should be in the Blättern, is written on it. Please take pictures of the inside of the keyboard and Post Them.
Are the keyboard and the usb ports working? If yes then look if they are still working when you plug out the battery. If everything still working then the battery is broken If it is Not working then you have a Chance to revive the battery
I've just bought the same keyboard with the same issue as yours... I've tried everything but it won't work-.- Could someone please check his battery of the keyboard with a multimeter and post here how much volts are on each connection of the battery and the connections on the board?