Product: Credit card or prepaid card

In XX/XX/XXXX, I applied for the XXXX XXXX Credit Card. My purchase was over {$2500.00}. I was approved for 0 % interest if paid for in 1 year. My credit score was excellent at over 740. Every month since then, I have made my payments on time. Last month ( XX/XX/XXXX ) I was going to pay off my card so that I did not get hit with the interest charges. As I was going to pay, I noticed a little drop-down menu where I can see any transactions on my card. I noticed that I was GETTING CHARGED INTEREST this entire time at 27 % WHAT?!?!?! I then called customer service and the customer service was great. The person agreed that it was a mistake on their end and was going to refund me the total amount of interest charges. She double checked to make sure that I was supposed to get the promotional APR and confirmed that I was supposed to get it. The total amount of interest charges is {$550.00}. I was also told that I should not worry about paying off the card because they were going to give me an extra year of 0 % interest. I was also ensured that it would reflect on my XX/XX/XXXX statement. I was very impressed with this solution. It is now XX/XX/XXXX, and the refund was not applied. I am also STILL BEING CHARGED INTEREST. I called customer support and it was a horrible experience. I am not sure what happened, but it was not the same experience that I had the first time. I spoke to an XXXX man who seemed confused and unwilling to help. I explained the situation and he put me on hold for almost 20 minutes. When he answered the phone, he said that I will be receiving a letter that tells me if I can get a refund for the interest charges or not. WAIT, WHAT?!?!?! I am surprised at this severe lack of communication and the incompetence of this company. I then ask to speak to a manager. After waiting for only 5 minutes, I am connected to a manager who immediately sounds irritated that she has to answer the phone. She answers by saying " I understand you have questions about the current promotions that are going on. '' I say " no ma'am, I am ... ... THEN SHE HANGS UP THE PHONE ON ME. I was left confused and shocked. I then immediately called them back and was connected to someone who sounded nice and was patient enough to listen to my explanation of the entire situation. She informed me that I am entitled to that refund of interest charges. She then checked the promotion from last year and said based on the amount I spent, I was entitled to 2 years of no interest. I was glad to hear this at this point I do not trust this bank at all. She told me it would take 1 to 2 billing cycles for me to see the charges refunded. At one point in the conversation, she offered me to take XXXX dollars which would be applied to my account within 48 hours in place of the refund which may take 60 days. This has got to be the shadiest bank I have ever dealt with. I declined respectfully and said I wanted what was rightfully mine which was a refund of the fraudulent interest charges. I then asked how I can know for sure that I will be given what is owed to me and she said that the nice person I talked to in XX/XX/XXXX did it wrong. She was insisting that she made a mistake in finding a resolution to this issue. Now, I am writing this report after a horrible experience with a bank that is not doing honest business.