Hi Manasa,
See we maintain the Business partner af FI customer with role as FLCU01 & some other for the customer details.
Check whether the details are different in both the roles..
Try to open the same customer in XD03 & BP, see whether there is difference in the region code maintained.
In the business partner there is validity of address whether the address validity has expired & it is picking from other address validity.
In my opinion your billing table should have sales area, as the tax classification is maintained at the level of sales area in customer master..
Regards,
Sachin Balmiki