There are, in fact, two balances kept for your account by most banks that have to comply with common convenience banking laws.
The first is your actual balance; it is simply the sum total of all deposits and withdrawals that have cleared the account; that is, both your bank and the bank from which the deposit came or to which the payment will go have exchanged necessary proof of authorization from the payor, and have confirmed with each other that the money has actually been debited from the account of the payor, transferred between the banks and credited to the account of the payee.
The second balance is the "available balance". This is the actual balance, plus any amount that the bank is "floating" you while a deposit clears, minus any amount that the bank has received notice of that you may have just authorized, but for which either full proof of authorization or the definite amount (or both) have not been confirmed.
This is what's happening here. Your bank received notice that you intended to pay the train company $X. They put an "authorization hold" on that $X, deducting it from your available balance but not your actual balance. The bank then, for whatever reason, declined to process the actual transaction (insufficient funds, suspicion of theft/fraud), but kept the hold in place in case the transaction was re-attempted.
Holds for debit purchases usually expire between 1 and 5 days after being placed if the hold is not subsequently "settled" by the merchant providing definite proof of amount and authorization before that time. The expiration time mainly depends on the policy of the bank holding your account. Holds can remain in place as long as thirty days for certain accounts or types of payment, again depending on bank policy. In certain circumstances, the bank can remove a hold on request. But it is the bank, and not the merchant, that you must contact to remove a hold or even inquire about one.