nokia n8 or chocolate fireguard

advice or help appreciated

bought my n8 of amazon sim free, had a problem with it and sent it back to nokia for repair, its came back locked to orange, as per nokia its had a new sys board in and its been set back to its original state,
spoke to nokia more than once nothing they can do, went into a orange shop to see if i could get it unlocked, they said no, emailed the company i bought it from on amazon, because nokia have changed the sys board he is saying its not the phone he sold me, how can i get this sorted,
all i want is my phone working again

please help

jds90 (joe)