Product: Credit card or prepaid card

Hi there - this is an odd situation and am not sure which category it fits in but hopefully you will understand better once I explain. 

I am a Saks Fifth Avenue Card holder which is backed by Capital One. On XX/XX/XXXX, I was in the store making a large purchase. The sales associate told me Saks was running a promotion on sales over {$2500.00} for zero interest for a year. She also said that I only needed to be a current Saks cardholder. I advised that as long as this would be a promotion applied to my current account, I would be interested but if it was a new account, I was not interested as I am buying a house and did not want any unnecessary credit or credit checks to affect my score. She assured me it was my Saks account and they would simply apply the zero interest to the balance of the purchases. 

I then purchased items ( charged over 3 days as the sales associate had to locate some items in other stores to ship to me ). After receiving the items, I ended up returning approximately 90 % of them. I received a Saks bill in the mail in XXXX for approximately what I anticipated my bill to be, which was {$2500.00}. The payments for my Saks card are automatically debited for the full amount every month, and given the sales associate advised the large purchase interest applied to this card, did not give the payment a second thought. The full balance of my regular Saks card was {$2700.00}, which was automatically debited and paid in full in XXXX. 

On XX/XX/2021, I received an alert from XXXX  that my FICO score had dropped due to a report of a delinquent payment. I had no idea what this was and when I looked it up, I found it to be for Capital One/Saks. When I called the 1-800 number I was told I owed {$280.00} on the new account I had just opened. I was shocked because not only did I not open a new account, I specifically told them not to open any new accounts. I never received a card or even a discloser or account number in the mail. When I asked the customer service rep for the account number for this new account, I was advised she couldn't give it to me and I would need to go to the store for them to look it up. I immediately paid the entire balance she said was due in the amount of {$280.00}. 

I have disputed the report with XXXX as I feel I was mislead by a misinformed sales person, who clearly didn't understand the program, however Capital one verified the charge and has refused to remove it. I have also written Capital one but have not received a response, nor am I hopeful it will be a positive one. 

Luckily, I am an essential worker and while I have worked through this pandemic to service others, I understand how lucky I am to have a job and not be asking for a payment extension. That said, I work very hard to ensure all payments are made on time and paid in full whenever possible. I would never look for a way to not pay for what I purchased. It makes no sense that I would pay a {$2700.00} bill to Capital One/Saks but then ignore a bill for {$280.00}. 

I am doing my best to able to maintain a credit score in an attempt to get the best rate possible for a mortgage. The very next day after reporting the delinquent charge, I began receiving notifications from credit card companies that they were lowering my limits as a result of this report. My score has plummeted and this will affect me well beyond the {$280.00} I immediately paid back. It is beyond disappointing and frustrating and it seems no amount of reasoning seems to resonate with Capital One. I never received a bill for the overdue amount in XXXX, and I am sure that {$280.00} includes late fees. If you can help me navigate this in any way possible, it would be very much appreciated. I am happy to provide you with any documentation necessary. Thank you so much for your consideration.