Yes, it means the same but we say "Te lo dije".

si, pero es te lo dije!

yes, could be "yo te dije", "te lo dije" or "te dije"

Yes it is correct, simple like that, people in the other comments are talking about litlle variations they use depending onthe country they live, Like if you say "I told you" while other people would say "I told you but you never listen"

This is how a Colombian mom would say it: "se lo dije y se lo advertí, pero no me hizo caso"