Calling stored procedure with return value

You need to add a ReturnValue-direction parameter to the command:

using (SqlConnection conn = new SqlConnection(getConnectionString()))
using (SqlCommand cmd = conn.CreateCommand())
{
    cmd.CommandText = parameterStatement.getQuery();
    cmd.CommandType = CommandType.StoredProcedure;
    cmd.Parameters.AddWithValue("SeqName", "SeqNameValue");

    // @ReturnVal could be any name
    var returnParameter = cmd.Parameters.Add("@ReturnVal", SqlDbType.Int);
    returnParameter.Direction = ParameterDirection.ReturnValue;

    conn.Open();
    cmd.ExecuteNonQuery();
    var result = returnParameter.Value;
}

Setting the parameter’s direction to ParameterDirection.ReturnValue instructs the SqlCommand to declare it as a variable and assign the stored procedure’s return value to it (exec @ReturnValue = spMyProcedure...), exactly like you would write it in SQL.