Motorola SLVR L7c
L7C MOTOROLA SLITHER PHONE
It sounds, though, like the phone was bought from someone else and there is a different security code set by the former owner. In this case, the phone either needs to be flashed (which is tedious business that requires reasearch before attempting) or needs to be taken to your service provider. I know that US Cellular can reset these codes, but I don't know who you are using. I wasn't charged a fee, but I also was the only owner and simply forgot my old code.
Sorry to not give you a way to do this on y...