C# and SQL update query

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C#

I have this code that should update a row in a table from a database.
The query works if I write it in SQL server directly as a query, but it doesn't work from a C# context. Can somebody please explain me what I should do to make this work:

this is my code:

//Pas huidig saldo kassa aan:
        public void huidigSaldoKassaAanpasser(int kassaID, double bedrag)
        {

            SqlTransaction transactie = null;
            try
            {
                if (connectie.State == System.Data.ConnectionState.Closed)
                {
                    connectie.Open();
                }
                transactie = connectie.BeginTransaction();
                SqlCommand cmdHaalGegevensOp = new SqlCommand(@"Update Kassa SET huidigsaldo = @bedrag
                                                                      WHERE id = @kassaID");
                cmdHaalGegevensOp.Connection = connectie;
                cmdHaalGegevensOp.Transaction = transactie;
                cmdHaalGegevensOp.Parameters.AddWithValue("@kassaID", kassaID);
                cmdHaalGegevensOp.Parameters.AddWithValue("@bedrag", bedrag);
                cmdHaalGegevensOp.ExecuteNonQuery();
               
            }
            catch (Exception ex)
            {
                if (transactie != null)
                {
                    transactie.Rollback();
                }
                throw ex;
            }
            finally
            {
                connectie.Close();
            }
        }

Unfortianetly everytime i run this code, I get no exceptions but the row isn't updated. The int kassaID and the double bedrag are correct.

If I write it as this in SQL server management studio as a new Query:

Update Kassa SET huidigsaldo = 598 WHERE id = 7;

everything works fine.