Regex
string input = "1-205-330-2342";
string result = Regex.Replace(input, @"[^d]", ""); //number only
// for anynumber from zero to infinity
[RegularExpression("^[0-9]*$", ErrorMessage = "Enter Valid Number")]
// for number greater than zero
[RegularExpression("^[1-9][0-9]*$", ErrorMessage = "Enter Valid Number")]
Actually I found the issue, I was validating the string during the TextBox object's creation, instead of when it updates so there was no way for that code to be executed when it was needed. My bad