Need a subsidy code for samsung u900?

i bought a samsung u900 off ebay that is locked on tmobile but i tried to put an orange sim card in it and locked it. i phoned tmobile up and they said i needed a subsidy code. but said i needed to prove i was the owner of the phone and want a mobilw phone number my address and pword. when i said i wasnt a tmobile customer they told me to get in touch with the person who sold it me but i have had no luck so i need a subsidy code badly or i have just wasted 180 quid.