Service tax invoice query for export of service

X Ltd (Service Receiver), Dubai Based Foreign Company dealing in food and beverage used to take promotion video preparation service for Social Media from Y Ltd (Service Provider), Mumbai based Advertising company. X Ltd paying all the bill in AED (Foreign Currency) for settling due till date. Till date all the invoices billed by Y Ltd in INR including Service Tax. Now my question is In which currency the service provider should billed the invoices to qualify its as a Export of Service from India & what we can do for the extra service paid by us all paid invoices which X Ltd did in Last Oct 2016? For your information - 1. There is not direct/indirect relation between X Ltd and Y Ltd. 2. Y Ltd VP Finance arguing that they will have to raise all the invoice in AED to qualify its as Export of Service. Can anyone help me on this ?