Cistern not filling up

I have no idea what you are talking about do you care to tell more about your situation??

When the arm with the ball falls, the other end rises leaving water come out. If it doesn't, you need to check the incoming line. The valve on the arm could be bad too. Not much of a deal to repair or replace. Finding the right parts may be tough. You may have to replace everything from where the water come sin to the arm. Only a cheapskate like Labman would mess around trying to fix the old one.

[chuckles at letmetellu]
A cistern is a vessel that holds water. This cistern is on a toilet. A modern toilet at that. Folks inside the border usually don't call it a cistern, we call it a tank.
The cistern filler upper is likely clogged with residue or debris, or someone may have turned the valve off.