My question involves a consumer law issue in the State of: North Carolina but the company is based out of Connecticut

On 1-22-2020, following a previous inquiry, I was contacted by the local retailer stating that they had a promotion I may be interested in. 1-23-2020, my husband and I went into the store to further inquire about the promotion. We were informed that they were offering free covers and 60% off of showroom models. During our first inquiry, we had an estimate drawn up for what we anticipated to purchase, they saved this document. On 1-23-2020, the employees present retrieved this estimate, reviewed it, and notified us that the previous employee had miscalculated and we would get a better deal by purchasing all new merchandise, not the discounted merchandise on the showroom floor. We chose to purchase 2 sectionals, consisting of new merchandise, and 2 bean bags, at a discounted rate, from the showroom. Upon confirming our selection the two employees began to calculate costs. They checked behind one another several times to confirm the price. Upon completion, we were presented with a total cost of $8,361. $7,500 of which was purchased with a credit card the retailer was promoting with zero interest, specifically for this transaction. Upon approval and completion of payment, the 2 bean bags were loaded in our vehicle, and we were told the remaining items, making up the 2 sectionals, would be delivered. 1-24-2020, I was contacted via text by the showroom manager stating that my order had been flagged. Upon calling, I was told that the store employees made a mistake and undercharged us, thus the items affected would not be shipped until we paid an additional $4,025. I was later informed this was the result of an error in the system that allowed them to add the promotion to the entire purchase instead of just a portion. After contacting corporate, and attempting to speak with the regional manager, I was told the best that could be done was to offer 20% off the affected items, a total of $3,461. My husband and I would have never initiated a transaction if it was at the additional total cost. This transaction was solicited by the store. In addition, by opening a line of credit, our credit has now taken a hit, that cannot be reversed. We paid in full the amount that was listed on the receipt which included the items in question. Are they required to honor this or are we required to pay additional money for the remain items?