Try this:
string test = @"!QUANT CMP=1,AMY=1,LIP=1,CBC=1,ESR=1,RF=1;!CALL W;ME6E;5466;;;!CALLED ME6E;5466!CALLED-;08/29/2013;09:59;ar;LDKH1;;W;!CALLED1 ME6E;5466;08/28/2018;23:31;ar;LT!CALLED1-LC1;;W;";
string pattern = @"!CALLED..?";
Regex r = new Regex(pattern);
test = test.Substring(test.IndexOf("!CALL ")+6, test.Length - test.IndexOf("!CALL ")-6);
var lines = test.Split(new string[]{" "}, StringSplitOptions.RemoveEmptyEntries)
.Select(x => r.Replace(x, ""))
.ToList();
foreach(string s in lines)
Console.WriteLine($"{s}\n");
Result:
W;ME6E;5466;;;
ME6E;5466;08/29/2013;09:59;ar;LDKH1;;W;
ME6E;5466;08/28/2018;23:31;ar;LTLC1;;W;