Product: Credit card or prepaid card

I 've been a faithful customer of Santander Bank since XX/XX/XXXX, when I opened a XXXX credit card with a promotional APR of 0 % for 24 month that expired around XX/XX/XXXX/XX/XX/XXXX. In XX/XX/XXXX paid the remaining balance of {$5700.00} in full ( which included {$110.00} of interest ) and in fact, over paid by {$4.00} on XX/XX/XXXX. The first payment for {$5600.00} was processed on XX/XX/XXXX leaving a remaining balance of {$110.00} on XX/XX/XXXX when I processed the final overpayment of {$110.00}. To my surprise, I received my statement today which showed an outstanding balance of {$36.00} ; an interest charge of {$40.00}, & the {$4.00} overpayment was credited to total leaving the balance at {$36.00}. 

I called Santander 's customer service line and explained to the customer service representative this was an over charge because I had cancelled the balance in full on XX/XX/XXXX and in fact over paid. The employee acknowledged this to be true but refused to issue the credit for {$36.00} to my account or file a dispute on my behalf, so I asked to be transferred to her manager who took the call and proceeded to re-verify my identity requesting my name, address, FULL Social security Number, phone number, date of birth and then asked my permission to view my credit report to continue verifying my identity which I agreed to. Upon asking me 4 additional security questions, one of which I was confused by, I responded with accurate information and she refused to assist me any further explaining I had to physically go in person at a branch to receive assistance with my account due to fraud potential on my account. When I asked her to clarify what this means and how this is possible she refused to explain, transfer me to her manager or escalate the call and instead transferred my call to the fraud dept. The Fraud Dept was unable to speak with me or assist me further. We ended the call and I called back and was told by the next representative and her supervisor XXXX, that there was a fraud alert on my account and the only way of removing this and getting customer service was by visiting a branch in person -- - even after explaining to her that I am XXXX XXXX and do not have the ability to visit a branch. Also, there are no branches in my area. XXXX then transferred me to his supervisor XXXX who repeated the same thing and insisted there was nothing she or anyone else could do to help me and that I 'd have to visit a branch in person. She proposed mailing in a notarized letter to their Fulfillment Office with my request, but explained I would still need to visit a branch in person because they do not follow up with customers after receiving these requests, and since my account had a fraud alert even if I called back to follow up with them they wo n't be able to speak with me over the phone or provide information about my claim/request due to the alert. I asked if there was a way of verifying my identity like the 1st representative did, with my name, address, full SSN, DOB, transaction history, or emailing/faxing/mailing copies of my ID + other proof of identity ( similar to the process the credit bureaus use to verify identity ) and she said no the only option is going in person. 

I told her I found it odd that when I applied for the credit card they were more than happy to process by phone without me visiting a branch or even providing proof of identification, suddenly when I have a claim about an overcharge to my acct, they give me such a hard time, making it inherently impossible to receive customer service and failing to provide XXXX customers with viable resolutions. I finally asked her to escalate my complaint and she offered to place one on my behalf which she did ( reference # XXXX ) however nobody has contacted/followed up in response. With each day that passes Santander will continue charging me 23 % interest upon the erroneous {$40.00} of interest I disputed in the first place, and I believe they know this and use this as a strategy to extort more money from customers who have paid them in full. Not to mention they are rudely insensitive to their customers and have no empathy for customer with medical limitations.