So I used the gameshark to get the old sea map but I cant use it when I go to littleroot town I can only go to slateport and battle tower can any one help me does any one know how to use this map or how to activate it?

1.) Are you using Emerald, or Ruby and Sapphire? I think it only works in Emerald.

2.) Aren't you supposed to go to Slateport, get on a Ferry, and tell them "Take me to Faraway Island"?
Also, which code did you use - the code to give you the map, or the code to give you the event for the map? I think the latter is usually the safer option.

Also check if it requires a mastercode, alot of people miss that.