Citibank Credit Card Complaint

Citibank Credit card department,

Billing disputes Texas

I went to purchase some items at Home Depot in -/-/- and made a Home Depot staff at check out who offered me a credit card with a promotion value worth $ - $40.00 discount on my purchase. I refused and offered to pay and leave but she insisted. I obliged her but after applying for the credit card she applied the discount of $40.00 and I paid the remaining amount at the desk. I did not get any credit card subsequently and did not make use of any credit card from Home Depot. However, I got this bill for $240.00 on the -/-/-. I called the number stated in the bill to clarify and I understood that the card is issued by Citi Bank. I was not satisfied by the response of the customer services rep I spoke to therefore I went to the Home Depot Store that offered me the credit card. They promptly discharged me by telling me that it is none of their business. I need to get this bill cancelled as I did not get any credit card neither have I made any purchase through a home depot credit card. My understanding is that the discount applied at the day I made the purchase was a promotional discount. I also do not want to take any credit card from Home Depot neither do I need a citi bank credit card at the moment.