How to validate data entry of a web service?

What is the best way to validate a WebService call? I explain: I have a WebService that has as Request a String of varying size and that returns the same formatted string, eg:

Input String:

  

"ST STN, SET J, * STORES T-40 / T41, - TER-REO, SHOPPING &   BOULEVARD KM 28,5 VALUE 450.00 CENTRAL. "

And that should return the String in the following format:

  

"ST STN CONJUNTO J LOJAS T40 T41 TERREO SHOPPING AND BOULEVARD KM 28,5   450.00 CENTRAL

Note: Decimal fields preserve Point and Comma .

That is, remove all Special Characters with EXCEPTION where Decimal Values , such as 28.5 and 450.00. p>

I have tried to do with Regex.Replace but without success and I am doing with Replace native C # , however with Replace it gets very complex as follows:

Here it replaces some characters (problem does not cover all characters):

string _texto = pTexto.Trim().Replace("S/A","SA").Replace("s.a.", "SA").Replace("S.A.","SA").Replace("S A", "SA").Replace("'","")
                                        .Replace("-", " ").Replace("&", "E").ToUpper().Replace("(","")
                                        .Replace(")","") .Replace("/", " ").Trim().Replace(";", "").Replace("N/C", "NC").Replace("\"","")
                                        .Replace("*","").Replace("+", "");

And with Regex I could not because Everyone removed the accents and characters of the sentence, the values Decimals lose the Comma or Point

String padrao = @"(?i)(,|.)?[^A-Z0-9]\s"; 
String padrao = @"(?i)[^0-9A-Z]\s]";

Regex rg = new Regex(_texto, " ");

var arrayTexto = resultado.Normalize(NormalizationForm.Formd).toCharArray();
                    foreach(char letter in arrayTexto) { 
                        if (CharUnicodeInfo.GetUnicodeCategory(letter) != UnicodeCategory.NonSpacingMark) sb.Append(letter); 
                        }

What is the best way to validate this string?