Nested if blank statement

COSTCENTER_fix = 

IF(
    ISBLANK('sapdata SAP_generalaccounting'[COSTCENTER]),
    IF(
        ISBLANK('sapdata SAP_generalaccounting'[WBS_ELEMT]),
        'sapdata SAP_generalaccounting'[PROFIT_CTR],
        LOOKUPVALUE('sapdata SAP_projektelement'[Ansvarigt_kostnstl], 'sapdata SAP_projektelement'[WBS_element], 'sapdata SAP_generalaccounting'[WBS_ELEMT])
    ),
    'sapdata SAP_generalaccounting'[COSTCENTER]
)

Here is my current code that is not working.

I want to check if column COSTCENTER is blank 
if it is blank use values from LOOKUPVALUE from WBS_ELEMNT
and if both are blank I want the values from PROFIT_CTR

problem is values from profit_ctr are not being entered, if both are blank this column is also blank. I cannot have blank rows in this column