Cannot Match Multiline String in C# Between Two Words

Question

I am trying to match the contents between BEGIN and END into a capture group called numbers from this string note:

   string note = @"BEGIN
   781-222-3311
   9789001122
   7817770000 to 7817770010
   END";

The variable I am putting the matched group value into is numbers. What I am using to match the string is the following:

   string numbers = "";
   Regex numberEncapsulationRegex = new Regex(@"begin\n(?<numbers>.+)\nend", RegexOptions.IgnoreCase);
   Match numberCatch = numberEncapsulationRegex.Match(note);
   if (numberCatch.Success)
   {
       Console.WriteLine("SUCCESS: \n");
       numbers += numberCatch.Groups["numbers"].Value;
   }

I have tried using RegexOptions.Multiline along with RegexOptions.IgnoreCase, and have also tried using:

   (?i:begin)\n(?<numbers\>.+)\n(?i:end)
   (?i:begin)(\n?<numbers>.+\n)(?i:end)
   (?<=BEGIN)(.*)(?=END)

Cannot get this to work. Thank you for reading and for helping, if willing.