NPS calculation at Company level

Really difficult to decipher what you are doing there, but if sometimes you return a blank when you really want to return 0, then this should work:

Relationship NPS = 
var NumOfRespon= 
CALCULATE (
	COUNTA ('Survey Response'[Relationship Likely to Recommend-Value]),
	FILTER('Survey Response', 'Survey Response'[Relationship Likely to Recommend-Value] <> BLANK() || 'Survey Response'[Relationship Likely to Recommend-Value] = 0 )
)

VAR thebombdiggedty = (CALCULATE(COUNTA('Survey Response'[Survey Name]),FILTER('Survey Response','Survey Response'[Relationship NPS Distribution]="Promoters"))/NumOfRespon-CALCULATE(COUNT('Survey Response'[Survey Name]),FILTER('Survey Response','Survey Response'[Relationship NPS Distribution]="Detractors"))/NumOfRespon) *100

RETURN IF(ISBLANK(thebombdiggedty),0,thebombdiggedty)