IF AND Statement with multiple condition

Need a formula that can retu values MET & NOT MET in Excel 2010

The formula MET or NOT MET at the resolution time.

Below is the formula I tried but something is missing, because not sure how to write an IF statement to compare IF the Date Close is "blank/open" and IF the SLA is still "within" the expected closure..the value should be "MET" and also another one how IF the expected closure date exceed the current date but still not closed..it should show NOT MET as the result.

IF(R13="","",IF(R13=0,"N/A",IF(AND(R13>0,U13=""),"NOT MET",IF(AND(R13="",U13=""),"",IF(V13<=R13,"MET",IF(V13>R13,"NOT MET"))))))