Product: Credit card

I had a Citibank issued CostCo Anywhere XXXX credit card through my membership with CostCo. I had this card for over 8 years and was never once late in my monthly payment. In fact, I linked my bank account with this card to automatically pay off the entire credit balance on a monthly basis since I have had it. 
In XXXX I received an email from Citibank saying I owed {$38.00} and was late on my payment. Upon closer review, I realized that there was an outstanding balance of {$8.00} on my credit card. For some reason, my bank autopay setup was disrupted on XX/XX/XXXX, a fee for {$30.00} was imposed by Citibank on XX/XX/XXXX, and a late payment email reminder was issued on XX/XX/XXXX. 
I called Citibank on XX/XX/XXXX and confirmed that, because the {$8.00} was not collected, Citibank decided to slap a {$30.00} fine on my account for the 3-day payment delay, regardless of the fact that my bank autopay disruption was neither caused by me, nor of my knowledge. 
I contested the {$30.00} returned check fee right away, citing the fact that although I cancelled my CostCo membership in XXXX and was told that I would lose the use of my Citibank credit card, never once was I warned, by CostCo nor Citibank, that my bank autopay arrangement would be affected. 
I immediately paid off the {$8.00} outstanding balance, requested Citibank to waive the {$30.00} returned check fees, and closed my credit card account in the same call. I thought me being such a loyal and well-behaving customer for over 8 years, this humble request would definitely be honored. 
Was I wrong! 
On XX/XX/XXXX, Citibank issued me another email saying my payment was past due. By then I have already traveled overseas to visit my family in XXXX. Very surprised I went back to check my closed credit card account, and found out not only did Citibank refuse to waive the {$30.00} returned check fees, but also imposed another {$30.00} late fees and {$0.00} interest charge onto my account, making the outstanding balance to more than doubled, rapidly growing from {$30.00} to {$60.00}! 
I had to call Citibank on international toll calls and spent over an hour explaining what happened to its service representatives. After several transfers and some long holding moments, I finally got to talk to a lady who was sympathetic and understanding enough. She said she was able to waive the newer {$30.00} late fees right away for me. As for the {$30.00} returned check fees and the {$0.00} interest charges she would need to write a report and get her supervisors approval. She said that she was hopeful such requests would be honored and she would write me an email to sum up all the issues. 
I never got her email. 
On XX/XX/XXXX, I received yet another Citibank email reminding me that my payment was past due. Surprised and much more in dismay, I realized that instead of waiving the {$30.00} returned check fees and interest charges as requested by its own service staff, Citibank added another {$30.00} late fees and {$0.00} interest charge to my account, pushing the outstanding balance to its all-time high, {$60.00}. 
What were all these about? 
I called Citibank on international toll calls again on XX/XX/XXXX. This time, it took me over 3 hours, staying up all night, trying to resolve the issue. Unfortunately, I was hung up multiple times by several Citibank staffs. Some of them obviously were not able to comprehend what I was trying to communicate. I called back time after time upon hang-ups, until I realized that there was no way I could get any justice with this bank. 
This is the background and, sadly, still on-going story of my very distressing experience with the Citibank credit card department and its servicing representatives. 
Unaware of the hidden traps that existed in the process designed and established by Citibank and CostCo, I turned out to be an easy prey of giant financial institutions like Citibank. 
But the question remains, why should I, a well-behaving yet powerless consumer, be so badly brutalized and sacrificed in a process so unfairly created by this giant financial institution to begin with?