Unable to get right value for correlation analysis

Hi everyone, 

I am unable to get the right value of correlation analysis when I analyze the data at month level. I have a data set that contains cases reported for 7 years. There are two different type cases category:

1. Good AFP cases

2. Normal

When I calcualte correlation of good AFP cases using a formula given in the attached file, it calcualtes it right at year interval. However, the value is not right for monthly interval at district level. 

I am attaching the files as well. Would be very really thankful if anyone can sort it out. 

Excel file (correlation is also calcuated)

POWER BI file (correlation calcuated that is not coming correct)