My bad, I had missed with the syntax and rewrote the first condition in a alternate manner and it fixed it. Thanks for your time to go through the post

The update code is for your reference

Select case {{ Month }} WHEN 0 then add_months(current_date(),-13 )  

WHEN {{ Month }} > month(add_months(current_date(),-1)) then add_months(to_date(concat(year(current_date())-1,'-',{{Month}},'-',1)),-13)

             else add_months(to_date(concat(year(current_date()),'-',{{Month}},'-',1)),-13) end