Product: Credit card or prepaid card

Hello my name is XXXX XXXX in XXXX I purchased {$7100.00} of Furniture form Mega Furniture. The store promotion was no interest financing until XXXX ( see flyer ). 
When discussing how much I wanted to pay I requested $ 250 monthly payments. We calculated it would take about 29 months, and with a 36 month agreement I could have it paid off early and have a cushion just in case anything happened. 
When finalizing the paperwork the agreement read only 12 months interest free when asked about the 36 months, I was in formed that the promotion is 12 months at a time and if I make my payments on time the promotion would automatically renew, that was the special financing ( see attached financing promotional ads ), reassured I signed the agreement. In XXXX I received the notice that my promotional financing was ending. I called Wells Fargo and they confirmed all my payments have been made on time but that does not renew the promotional terms I was advised to contact the store. 
I contacted the store spoke to XXXX my salesman and he said he should renew, he then went and spoke to his manager who said she would have to look up the agreement and call me back. 
When she called me back she informed me that they no longer work with Wells Fargo for financing and the agreement says it was only for 12 months. I explained to her that is not what I was told when I signed it and XXXX just confirmed that is should automatically renew. She apologized and said he did not understand the question. But there was no question it what he told be a the reason I agreed. To pay off that amount in a year I would have had to pay over {$600.00} a month which I would absolutely not be able to agree to as I could not afford that high of a monthly payment. She again apologized for the confusion and advised there nothing they could do. 
Distraught I called Wells Fargo back and again explained the situation and was advised all I could do was dispute this. This is my second dispute I contacted the XXXX  and was replied to by XXXX XXXX who I also spoke to. I advised her of the situation and that Wells Fargo has been great with working with me and advised they will change the terms XXXX XXXX just need to submit a Terms Change Request Form. 
XXXX requested that Wells Fargo send them the form as they are no longer vendors. XXXX Wells Fargo sent it over the same day and XXXX confirmed it was received and she would forward it to accounting. I followed up a week later XXXX advised me there were items on the form that they did not know as they are no longer vendors she requested Wells Fargo contact them directly to help complete the form so they can submit it. XXXX Wells Fargo called the same day. XXXX thanked me for getting Wells Fargo to make the call and the form will be completed. Confirmed with Wells that they spoke and gave all the information to complete the form. I agreed to close my XXXX   complaint. Only to find out after it was close XXXX XXXX contacted Wells Fargo and said they will not be changing the terms. I contacted the XXXX to advised of the matter and am trying to get the claim reopened. 
I have made every payment to pay the original amount ( no XXXX XXXX in full in under 3 years. 
I am asking XXXX XXXXXXXX to make this right and submit the change in terms from 12 months to 36 months. 

Please help me. they are trying to charge me {$4800.00} in interest. 

Thank you, XXXX XXXX