Tata Indicom — Need of purchasing Modem compulsorily with Tata Indicom post-paid SIM for Internet access

I already have a USB modem (from Tata Indicom) which was purchased by my brother along with a post-paid sim card for Internet access. The sim card was surrendered by him as he no longer needed the connection.

Now, I have the USB and I am planning to purchase a post-paid SIM card in Pune for internet access. But the company representative is insisting on buying a new USB modem again as it has been decided by the company management that not to give post-paid card without USB modem.

Now, why should I purchase a USB modem when I already have one which was earlier purchased from Tata Indicom?

I think Tata Indicom is trying to setup means of earning money in such a way.