Billing Block will not work if you did not assign it

Define the possible block indicators in SM30 - V_TVFS 

and 

allocate them to the billing types concerned in SM30 - V_TVFSP. 
 

Your Billing Block will not worked if you did not assigned it to the desired billing types. 
 

You can auto block by :- 

1.  sales document type in transaction VOV8, fields Billing Block,

or

2.  item categories in SM30 - V_TVAP, by filling the fields Billing Block.