String.Insert not working [duplicate]

Answer 1

I'm such an idiot, instant Google search fixed this.

String.Insert does not modify the string it is called on, but instead returns a new string with the inserted text in.

So I needed:

String = String.Insert(0, "test");

Answer 2

it should work

see the below example

string names = "Romeo Juliet";
string shakespeare = names.Insert(6, "and ");

Console.WriteLine(shakespeare);

the result will be Romeo and Juliet

see the fiddle