Correct

空号

/ kōng háo / 
Strokes

Definition

disconnected phone number/unassigned phone number

Example

As a Noun

out-of-service number

1
Duìbuqǐ
对不起
  
,
nín
您
bō
拨
de
的
hàomǎ
号码
shì
是
kōngháo
空号
  
。

Sorry, the number you dialed is not in service.