Downgrade SBS 2011 keys to SBS 2003

Hi

We have recently brought 6 X 5 user CAL licensing for SBS 2011 OEM and we wish to downgrade the licenses for SBS 2003, I have spoken to Microsoft licensing team and they only gave me a key for 20 users and refused to downgrade the other licenses.

Please let me know if we can downgrade the other CAL packs as our clients need more licenses.

Many Thanks

Mahesh