Oak Ridge Apartment charge, lie, Internet

Im living in Oakridge apartment, Austin, TX.  Several weeks ago, I made an electric payment for water bill using the apartment website, and I found out that I mistyped my bank account number; so I made an electric transfer again with using the correct account number. Both transaction (one failed, one successful) made much before the due date, and I also had enough prepaid amount.
 
This morning, the apartment office noticed me that I need to pay extra $25 because I mistyped the account number once. They said that the bank charged them the wrong transaction fee.
 
I couldnt understand that, so I checked with my bank (BoA) and they told me that they never charged with wrong account number. So, I figured out that they were lying and trying to charge me with nothing. (this kind of things happened few months ago too)
 
So, I went to the apartment, and then, they said the contract says I should pay extra $35 for returned check or rejected electronic payment in the clause 6.
 
I can see that too, but what it means in the clause is that if the transaction could not be made after the payment of the rent; and one failed to pay the RENT before the due date (because of wrong check), one should pay extra $35 for that; not for making a mistake with the account number and successfully paid right after that.
 
I think they try to rip me off; and this is really unfair. They cannot just charge me and threat me. How can I resolve this problem?  Thank you.