Old iPhone is Being Associated W/ my New One

My brother is using my old iPhone 4. I have a new iPhone 5. He has a different phone number than me and he bought a new sim card.

I got a message that his number is now associated with my email? Whatever is happening, our phones are crossed. We get all the same messages, his contacts are synced to my phone and vice-versa, same with photos. I am going crazy.

I am not in the same city as him, I cannot see what he is doing on it to make this problem happen.

Please HELP.