EZ-Link Reload Error or Pre-authorisation Deduct

My ezlink card balance is $8.28 as at 23 Aug 16. My last used of this card is on 12 Aug 2016

However on 17 Aug 2016, I received a SMS from bank that there is a transaction of $50 charge to my credit card from the ezlink.

This has made me worried that there is an unauthorise usage of my credit card.

According to the ezlink reload FAQ 

Auto top-up occurs when the remaining value is insufficient for the next payment transaction. My ezlink balance is more than $8 is more than enough.

Q15: When and where does auto top-up occurs on my ez-link card?

Once the EZ-Reload facility has been activated on an ez-link card, auto top-up occurs when the remaining value of the ez-link card is insufficient to pay for your next payment transaction when used on any train gates, bus devices for payment.

Example: Assume that you have activated the EZ-Reload facility on your ez-link card for $30.00, and there is a remaining stored value of $2.50 on your ez-link card and the journey cost $2.70:

• When you tap your ez-link card at a train gate, the auto top-up will occur, because there is a minimum required remaining value of $3.00 on entering the train gate. Hence when you exit, the new value of your card will show $29.80
• When you tap your ez-link card at a bus device (e.g. Express Bus service), the auto top-up will occur when you exit as it has calculated that the total journey is more than the value left on the card, hence the new value will be shown at the EXIT bus device will be $29.80.

I launch a complaint to my bank credit card on this "illegal" transaction and today I got an answer. Under the term and conditions of the ez-link Ez-reload, the ez-link will obtain and hold the pre-authorisation amount if the ez-link card valus is less than $20 and not what stated in the FAQs. So there is no error on the above transaction.

EZ-Link shall be entitled to obtain and hold a pre-authorisation (“Pre-authorisation”) equivalent to the Revaluation Amount and Convenience Fee from the Card Issuer and will be held by EZ-Link for a period of 7 calendar days to be applied towards any pending Revaluation when the Stored Value of the EZ-Reload by Card Enabled ez-link card reaches a value of S$20.00 or less. The Account Holder acknowledges that the Pre-authorisation will not be available for use from the Account until either the Pre-authorisation is applied towards the Revaluation or where EZ-Link releases the Pre-authorisation back to the Card Issuer if no Revaluation occurs within the 7 calendar days. The Account Holder acknowledges that notwithstanding that EZ-Link has released the Pre-authorisation, the amount will only be available for the Account Holder’s use after the Card Issuer has effected the release of the amount into the Account;

This has caused a confusion to the consumer if they did not read the fine print on the term and conditions. To make it more transparent to consumer, this value less than $20 should be also in the FAQs.

I the the NETS Flash pay ATU also has this condition list as I always receive a SMS from the bank on the ATU as my NETS Flash pay card balance is less than $20.