TANs (Transaction Number) can only be used for personal transactions. Your bank will never ask you to enter a TAN for prize draws, security updates or to refund money to your account. Hence, please always use caution if you are asked for your bank details or a TAN when you are not actually making a transaction.
Once a TAN has been generated, your chipTAN generator or mobile phone will show all of the main transaction data again alongside the TAN. If these data do not match the data you entered, cancel the transaction and immediately get in touch with your Sparkasse.