@Acecatmum: With Fast Charging enabled, please tap the Side Key to place your phone in an idle/locked state, then connect to your official Samsung charger via a power outlet. Does 'Fast charging' appear on screen momentarily, before reverting to 'Charging'? Alternatively, if you head to Settings > Battery and device care > Battery, does it say 'Fast charger connected' below the progress bar at the top of the screen?
