Their meanings are all depending on the context .
For example, 没用=没有用
1) as an adj,,, it means something is useless or somebody is incompetent / not productive in a team
2) as a negative term of a verb, it means " I didn't use it / I haven't used it"
-------How do you like the shampoo we bought the other day ?
-------Oh, I haven't used it yet . <我还没用。>
AS for 不用了 , when someone's trying to help you or do something for you, and you don't need, you could anser "不用了", meaning "don't bother, I don't need it. " When it refers to something you used to use, but don't wanna use it anymore, you could say "我不用了”，meaning "I don't use it anymore."