Product: Debt collection

This is regarding the purchase of item on XX/XX/XXXX for {$370.00} at Home Depot using a Home Depot Consumer Credit Card issued and serviced by Citibank, N.A.. 
The day of purchase I was told by a Home Depot associate that the item was on sale and that if I applied for a Home Depot credit card and paid for the item with the new credit card that there would be special financing on the item. I would not have to pay any interest on the item nor pay for the item for 6 months. I specifically asked the associate if I needed to pay anything within the 6 months. The associate replied " No '', just pay the full amount in 6 months. So I believed that no payment for this one item was required until XX/XX/XXXX. I applied for the credit card and used it to purchase the item as well as one other item. The first bill that I received is attached ( pages 1 thru 3 ). The total amount is for {$400.00} ( {$370.00} for promotional item and {$31.00} for a second item ), it is page 1 of the attachment. Minimum payment was {$27.00}. I sent a check in the amount of {$31.00} to cover the full cost of second item purchased. I did this to ensure that there would be no interest charged on the first purchase. I then ignored all further bills since it was my understanding that no payments were required until XX/XX/XXXX. 
The next time I became aware of this issue was upon receiving a letter from a collection agency - XXXX XXXX XXXX XXXX - around XX/XX/XXXX. See page 4 of attachment. I promptly called them and explained that it was my understanding that I did not need to pay the {$370.00} until XX/XX/XXXX. They did not have a copy of the bill, so I faxed them the page and noted that I did not have to pay until XX/XX/XXXX. In the interim I paid the {$370.00} for the item ( shown on page 5 of attachment ) before the XX/XX/XXXX due date. 
I contacted XXXX XXXX again on XX/XX/XXXX. They said that my dispute was rejected and that I would have to pay all fees and interest charges. They told me I should have read the fine print. If I had to read and understand every fine print on every transaction that I make, I probably would not buy anything. I wonder how many sales associates would be able to explain the fine print to me? 
Well I did read the bill and fine print. This is what I found : A ) In the middle of the first page ( 1st page of attachment ) of the bill it reads " You must pay your promotional balance of {$370.00} in full by XX/XX/XXXX to avoid paying deferred interest charges. ". So I thought that the only payment I needed to make was this amount in XX/XX/XXXX. 
B ) In upper righthand corner of second page of bill ( 2nd page of  attachment ) under heading " How to Avoid Interest on Purchases '' second paragraph it states " If you have a balance subject to a deferred interest or 0 % APR promotion and that promotion does not expire before the payment due date, that balance ( the " excluded balance '' ) is excluded from the amount you must pay in full to get a grace period ''. Again it seems to me that I needed to pay the amount before XX/XX/XXXX. 
C ) On the third page ( 3rd page of attachment ) of the bill under " TRANSACTIONS '' it states " PROMOTIONAL PURCHASE : To avoid interest charges, please pay the above in full by XX/XX/XXXX. Monthly payments required. ". I just noticed this as I was creating this dispute. Still not clear what monthly payments mean as it relates to this transaction. 
D ) On the third page ( 3rd page of attachment ) of the bill under " ACTIVITY AND PROMTIONS DETAIL '' there is a column headed " Promotion Minimum Payment Due ''. The amount shown is {$0.00}. Again I have to believe that the only payment that I have to make is for the full amount in XX/XX/XXXX. 

This entire bill for this transaction is confusing to me. I am XXXX years young. I have made many transactions in my life time. Many more complex than buying one item at Home Depot with a Home Depot charge card. I have never had an issue such as this or a more confusing transaction. If I had known that I had to make monthly payments, I would have paid the entire bill at once ( not a huge purchase ). I am requesting a waiver of all interest charges and fees ( {$140.00} shown on page 5 of attachment ).