How to validate charcter between number range

Hi experts,

My number range is from 'AA00000001' to 'ZZ99999999'.

if i am passing number 'BB12131234' and this series exist in renge given above

SO according to my code its showing out of range.

 if number between 'AA00000001' and 'ZZ99999999'
*      NUMBER IS IN RANGE
      return-message = 'Customer Created Successfully'.
    ELSE.
*     NUMBER IS OUT OF RANGE
      return-message = msg.
    ENDIF.

So how i check my series in the range

thanks