Different output from stored procedure in SSMS and ASP.NET - asp.net

Question

I created a stored procedure to include a new user for my system. Parameters are: Name, Mail and Password (all varchar). The stored procedure first checks if the mail is already in the database. If not, then the information in added to the table. At the end, the output is a table with the user data.
CREATE PROCEDURE [dbo].[user_new]
(#name VARCHAR(50),
#mail VARCHAR(50),
#password VARCHAR(100)
)
AS
BEGIN
SET NOCOUNT ON
DECLARE #exist INT
SELECT #exist = COUNT([id])
FROM [dbo].[User]
WHERE [mail] = #mail
IF #exist = 0
INSERT INTO [dbo].[User] ([name], [mail], [password])
VALUES (#name, #mail, #password)
SELECT
#exist AS [exist], [id], [name], [mail]
FROM
[dbo].[User]
WHERE
[mail] = #mail
END
GO
When I execute the stored procedure in SSMS, everything works fine: when I insert a new mail, field [exist] returns 0. When I insert a mail that already exist, field [exist] returns 1. So far, so good.
When I execute the stored procedure from my .NET application (which has a lot of other calls that are working fine), the error happen: no matter if I try to add a new or an existing mail, [exist] always returns 1. I tried to change the logic several times, but I always get the wrong result.
Here is the .NET code:
Public Function api_v2_player_new(<FromBody> s As User) As Object
Dim arrParameters(,) As String = {{"#name", s.Name}, {"#mail", s.Mail}, {"#password", s.Password}}
Dim dtc As Data.DataTableCollection = SQL.Execute("dbo.user_new", arrParameters)
Return SQL.toJson(dtc(0))
End Function
Public Class SQL
Public Shared Function runStoredProcedure(ByVal cmd As SqlCommand) As Data.DataTableCollection
Dim spName As String = cmd.CommandText.ToString
cmd.CommandTimeout = 120
Dim cs As String = System.Configuration.ConfigurationManager.ConnectionStrings("csKickerliga").ConnectionString
Dim connection As SqlConnection = Nothing
connection = New SqlConnection(cs)
Dim dt As DataTable = New DataTable()
cmd.Connection = connection
connection.Open()
Dim adp As New SqlDataAdapter(cmd)
Dim ds As DataSet = New DataSet()
cmd.ExecuteNonQuery()
adp.Fill(ds, spName)
Return ds.Tables
connection.Close()
End Function
Shared Function Execute(spName As String, arrParameters(,) As String) As Data.DataTableCollection
Dim cmd As SqlCommand = New SqlCommand(spName)
cmd.CommandType = CommandType.StoredProcedure
With cmd.Parameters
For i = 0 To (arrParameters.Length / 2) - 1
.AddWithValue(arrParameters(i, 0), arrParameters(i, 1))
Next
End With
Dim dtc = runStoredProcedure(cmd)
Return dtc
End Function
Shared Function toJson(dt As DataTable) As List(Of Object)
Dim oList As New List(Of Object)
Dim o As New Dictionary(Of String, Object)
Dim data As Object
For Each r As DataRow In dt.Rows
o = New Dictionary(Of String, Object)
For Each c As DataColumn In dt.Columns
If IsNumeric(r(c.ColumnName)) Then
If Not r(c.ColumnName).ToString.Contains(".") Then
data = CInt(r(c.ColumnName))
Else
data = r(c.ColumnName).ToString
End If
Else
data = r(c.ColumnName).ToString
End If
o.Add(c.ColumnName, data)
Next
oList.Add(o)
Next
Return oList
End Function
End Class

Answer 1

Found the issue. The code was executing the stored procedure twice:
cmd.ExecuteNonQuery()
adp.Fill(ds, spName)
Therefore on the recond run the record already existed because it was created on the first run. I removed one of the lines and now it's working!