If water continues to emerge from your shower once the it has been switched off, it typically indicates a problem with the cartridge.
Shower cartridges are incorporated within the shower system, and they are a device responsible for shutting off water flow and the levels of hot or cold water that exit from the shower head or tap.
The cartridge will inevitably wear out over time and will require replacement. This is likely to be the case if your shower won’t stop running.