I provide support to one uk company from india (as freelencer). they need legal invoice to pay for my services. please assist.?

They will pay me monthly (on per hour basis) against the invoice which I will send them. However, they need legal invoice which should have any TIN or any number which is genuine asper india law (but NOT VAT). I do have PAN card. How can I provide them a legal invoice with which number? How to get TIN or service tax number etc.I do not have any company and i support them by myself. Please assist.Do I need any CA and how much charge will be applicable on my case?