Cal day not sorted as date

I have a pivot table and a chart based on calendar day field which does not get automatically recognized as date in Analysis for excel  version 1.4.11 .

I have seen in forums that it is a known issue and tried basic trouble shooting such as converting the column to date field,  text to column etc  which went in vain.

Source of pivot is the bex query output and this report is dynamic.

Because of this,  the calenday day entries are sorted  as below

But in my data sheet which is the result of bex query output which serves as input to pivot has sorted calendar day chronologically.

Any idea on how to fix this?