God had forbidden to talk to Samuel by legal means (1 Samuel 28:6). What makes you think God would induldge Samuel by illegal means? It was forbidden (illegal) for God's people or Saul to contact mediums, etc. This would be a violation of God's Word (Leviticus 19:31). Also, it would show that ghosts are okay and can be real and trusted. But remember when the rich man's request was refused to visit his brothers to tell them of the place of torment that he was in? (Luke 16:31). Also, Saul never actually seen Samuel. He was asking the medium what he looked like (1 Samuel 28:13). Only the witch had seen this vision of Samuel. But what about her being shock and surprised? Well, you have to remember that Satan can appear as an angel of light and his ministers into the ministers of righteousness (2 Corinthians 11:14-15). Also, the entity's prediction did not come true, either. The thing communicating with Saul told him in 1 Samuel 28:19 that he would be delivered into the hands of the Philistines. Yet, this did not happen. Saul took his own life before he could be taken into the hands of the Philistines (1 Samuel 31:1-4).
As for the Bible referring to the entity as Samuel: Well, we have to understand that there are other occurences in Scripture whereby a name ascribed to somebody is not an exact description of that person or being at first glance (Unless of course we dig a little deeper into the meaning of the use of that word). For example: Scripture says, "Ye are gods." Jesus used this quote in Scripture to deflect unbelieving Jews when He made a reference to His divine nature (as God). Also, Jesus Himself appears several times in the Old Testament. He is called the "
Angel of the Lord" or the "
Messenger of the Lord" in the Old Testament (See this thread
here at CF). However, this does not mean Jesus is an angel or anything. Jesus is uncreated and eternal and Jesus is the second person within the Godhead or the Trinity.
The Spirit of God departed Saul and an evil spirit came upon him because he sinned; So Saul broke God's laws even more by contacting a sorcerer and then committing suicide. Both are grevious sins. Saul was not saved in the end because of this. Be not deceived, the unrighteous will not inherit the Kingdom of God.