I ordered a Samsung 451 but received a case for Samsung 450 why?

You will not have any problems if you have a Samsung 451 but the case you received says Samsung 450. Both these phones are exactly the same. What makes them different is the cellular provider that markets them. The Samsung 451 is sold by Straight Talk Wireless and NET10 Wireless and Samsung 450 is sold by Metro PCS and other providers.

Both these phone models are exactly the same.