Problem with PPPOE

Im usgin a microtik for a PPPOE server , the thing is that wen i assign a local address/remote address ip to a user created , another user that dont have any ip assign to local address/remote address gets the same ip , i will like to now how to attach and ip addres to a user and no other user can get that ip address from the PPPOE.

anyone?? help me !