Same thing happened to me a few weeks ago and I believe your MSL code was changed and not even Sprint can help you figure it out. First, you might need to re-provision the Internet back to your phone. Three options are available.
1.- Dial, ##3282#, then hit Edit, it will ask you for your unlock code (I think this is the same as your programming code.) First Use this program below to retrieve your unlock code, Install it on the Device memory, run it and follow the instructions. Once done go to ##3282# follow the scenario as presented previously, hit restore. It will ask you to soft-reset, follow the rest. This should help. If not, move to option 2.
2.- Manually setup your internet connection. When you dialed ##3282# and hit Edit, you`ll get to a screen that displays a few characters. Make a note of Username which should be in this format;
USERNAME@sprintpcs.com and then note the one that says AAA Shared Secret that is your Vision Password.
Now go to setting/connection/manage connection. Then click Edit or create new connection. Follow the instructions.
3.- The manufacturer Hard-Reset is a last resort. Dial ##786#, enter your unlock code retrieved by the BAFMSL software from the beginning. This should take your phone to the manufacturer state. That should resolve whatever the issue at last. Then, flash Sprint Stock ROM so that you may get your account settings back to your phone. Afterwards you may flash back to whatever custom ROM you will.
PS: These procedures are for Sprint phone. Hope it helps.