Why is the base currect incorrect?
The base resistor multiplication effect that you used in your calculation happens because the base emitter (R4 in your circuit) increases voltage both due to the base current and due to the collector current. So in order for the this effect to be what you expect, the transistor has to be in forward active mode. But here, the transistor is in saturation.

Consider if the transistor were forward-active and the base current were 8 uA. Then the collector current would be 2.3 mA. Then if there were 2.3 mA through R5, the collector voltage would have to be -227 V. Since the transistor isn't a power source, this can't happen, and we know the transistor is saturated.