Product: Credit card or prepaid card

I learned yesterday XX/XX/XXXX that my interest-rate was chanfed without my knowledge to a variable interest rate currently almost 11 %. When I got my chase Slate card more than 10 years ago I agreed to a fixed interest rate card of 8.9 % with a introductory special that was likely 0 % but the fixed rate on the card that I agreed to was going to be 8.9 %. I only get credit cards with fixed rates. I have called in the past asking if I could reduce my current rate thinking that I had my 8.9 % rate still not knowing that it was printed on statements. I was told by customer service and also a manager at the call center yesterday that I was sent a letter in XX/XX/XXXX so eight years ago that they were going to change my interest-rate to this variable rate. They told me that in the letter it gave me the option to opt out close my account and continue paying my card with my existing rate or to opt in I did not have to do anything it would be automatic. The problem is I never received this letter. I don't know if it was because I was in the process of moving or if because it was missed delivered by the post office. I feel it is highly unethical to automatically a person into paying a company more money without something more than a letter. It was not a certified letter. There was no phone calls. And well it could be argued that I always had the ability to check my rate, when I signed up for a fixed rate card and there is nothing that would ever make me think that I would need to check for any changes. I knew that as long as I was never late my interest rate when I change. When I called to complain that people have. I asked for an executive contact to make a formal complaint and was told that I can not be provided with one. I was I also asked and ask for help while the representatives were kind a professional they also dismissed me telling me that my rate was still good compared to other rates that people have. I asked for an executive contact to make a formal complaint and was told that I can not be provided with one. I asked who my complaint would be communicated to and got a vague answer and when I asked if I would be contacted regarding my complaint I was told no. I also asked that the amount of excess interest that I paid over the course of these eight years be calculated and refunded to me and that I would choose to opt out clothes my card and pay it off. They told me it was impossible for them to calculate that figure. In my own estimate calculation I believe that amount was well over {$2000.00}. That's {$2000.00} in unnecessary interest that I paid that I feel I was tricked into paying them. I feel like I had money stolen from me. I am sure that I am not the only one that this happened to so I will be telling as many people as I know that think they have fixed interest rate cards especially with Chase because they told me that they changed everyone to variable interest rates to definitely check on it. This is a very unethical way of doing business and I just want to be compensated for the money that was taken from me unfairly and to close my card. Ideally I would like to close my card sever ties and pay nothing back because I feel this was a criminal act against me but whatever can be done I am open to negotiation. Thank you for taking the time to hear my complaint.