Company assignment overseas compensation greviances

I have been sent to Italy by my company on assignment and was promised Euro 2297 per month for expenses plus company paid rental car and furnished accomodation over and above my existing salary in India. The contract also states that any additional taxes due to the assignment as compared to my tax situation had I remained in India shall be borne by the company. After coming here I am told that the entitled Euros will be paid in INR along with Indian salary to account for taxes. On one hand I am advised to use my International debit card linked to the salary account for expenses in Euros while they insist on paying the INR equal to 2297 Euros at a much lower exchange rate causing a loss of 4-7% for every Euro spent here. This loss will run in excess of INR 2 Lakh in a span of one year. On taking up this matter with the concerned finance department, I am told that it is as per company policy and nothing can be done regarding it. No details about this policy was provided before sending me on assignment in spite of several requests from my side. Please help.