Product: Credit card or prepaid card

In XXXX I received a letter from Capital One however I did not understand this letter. I could not find a definition of some of the terms found in this letter. I called the company and was told, there were changes being made to the laws regarding credit cards and Capital One was changing the terms of the contract to be in line with those new laws. I asked at that time about the interest rate. I previously had a fixed rate of 9.2 %. I was told at that time my interest rate would be fixed moving forward. I was assured it was part of the new law and was assured that it would be fixed. For sometime after this I periodically checked the interest that I was being charged and it did not change. When I opted for paperless billing I was no longer able to see the interest rate however believing it was fixed I really had no reason to look. Over the years I based my spending habits on that interest rate calculating the payment I would need to keep my balances at reasonable levels. 

Fast forward several years. XX/XX/XXXX XXXX I was reviewing my balances trying to figure out why they were still higher that I had calculated. After clicking around a bit I found the problem. The interest rate was charging higher than expected. I called Capital One to have them recalculate my interest as I believed my rate was fixed at a lower rate than what they were charging. After speaking with them I was informed my contract indeed specified a fixed rate of 9.2 % and I was currently being charged higher than that rate. I was placed on hold and transferred to a new person. This person told me that my rate changed in XXXX. I asked for documentation. I was also told there were no notices found about a change in interest rates. I told them about the letter I received in XXXX and the phone call with them at that time that assured me my rate would be fixed. They said they could not do anything about the past but they could lower my interest rate back to the agreed upon rate temporarily. I made the comment about Capital One commercials back in the day and I felt this had been false advertisement. At this point I had to return to work as it was XXXX so I decided to get off the phone and call back later. 

I called back XXXX and asked for a copy of the letter that they say changed me to a variable rate. I was asked where I wanted the letter sent. I provided my email. I was placed on hold, placed on hold again, placed on hold again, then told they couldn't find it. I asked them since they couldn't find it they could switch my rate back to fixed and recalculate my balances according to the agreed upon contract in their file. They refused. I was placed on hold and then spoke to the supervisor and asked again for the letter. I was placed on hold, I then spoke to the Supervisor again and stated, If the letter notification could not be produced then my accounts should be audited at the fixed interest rate and adjusted accordingly. I was placed on hold again but then when he came back abruptly told I would receive the letter in the mail in 7 to 10 days and was offered no further explanation. I attempted to gain information about the letter as to what I believed it had said but no explanation was provided there was just a long pause. When the supervisor came back after the pause he ended the conversation. 

So many questions. Why I was told in XXXX the rate would be fixed? Why did it stay at the fixed rate for so long after XXXX? Why did it take an hour to find the letter, was the letter actually found? If it was found why it can't be sent by email? Will I really receive the letter that was sent in XXXX or if it will be a fake? Was what happened in XXXX was legal to begin with?