need help urgently

[blu38ear]

hi i have a iphone 3gs, i tried unlocking the phone i got told i needed to put software 4.1 with baseband 6.15.00...which i have done...i come to downgrade my baseband to the 5.13.04 i think?....so i can unlcok my phone...but wouldnt work someone said put ios 5.1.1 on and trry again so i did....and i still cant downgrade my phone?..can someone please help me as i dont know what to do and i have no service either