Want to use Boost Phone i425t (Pay as you go) with...

Question

I ran over my Nextel phone I did not have insurance. They were going to charge too much to replace it. SO I purchased the Boost i425 prepay phone at Walmart b/c it stated on the pkg. Nextel. But when I place my SIM card in it asks for the special code. 8 digits. I contacted Nextel and they gave me my code for my SIM card, but it said it was invalid and locks me out after the 3rd try. Does anyone know how I can make this phone work with my SIM card?
Thanks for any help!