Product: Credit card

I purchased a XXXX at Mattress Firm. The sales rep told me I can pay off the purchase over time without interest. I did not realize that what was happening was that I was opening an ordinary credit card. I thought that I was getting a finance plan which I set up so that the payments can be taken from my bank account every month and that Mattress Firm was who I was conducting this financing plan with. I was not told from there that if I did not pay the total amount by a certain deadline that interest from the inception of the purchase would be applied. 
As months passed I thought I set up the plan so that when the debt was paid it would stop taking a withdrawal from my bank. After some time, I realized that I was still paying this debt and it should have been over by then. I did get monthly emails from " Synchrony bank/Mattress Firm but I did not give it that much thought because the Payment plan was " set up. '' I saw at some point that the amount I owed was the SAME amount that I started with, over {$3000.00}. I logged in to the online account and I then came to understand that I was charged over {$1900.00} in interest as of XX/XX/2023. This entire time I had not had a finance plan with this vendor but rather with this unscrupulous company giving me a promotion of what is known as deferred interest. They have charged me as of XX/XX/2023 over {$1900.00} of interest going back to the beginning of the original charge! I was extremely upset as I felt misled by the sales team at Mattress Firm that it was interest free. Interest free is not deferred as I now understand. 
The experience is very misleading and as I go back to look at the purchase document from Mattress firm, there is a document that is only one paragraph that tells me about this deferred interest which was NOT explained to me. The misleading part here is that unsuspecting consumers are under the impression that there is interest free and set it and forget it, but the reality is you are hit with a huge penalty of deferred interest when you don't meet their terms. 
I feel cheated and misled with this. Why would Synchrony have the logo of Mattress Firm on their emails? If they are not Mattress Firm, don't advertise that you are because you give the impression that the financing is truly from the vendor and not a credit card company hoping to collect on deferred interest from unsuspecting consumers. This type of promotional dealings are crooked and they have to stop. Now I owe the same amount as I started with so none of the payments I made through their " promotional period '' count towards anything! It's like I never paid anything and they get to charge me and take advantage of me. 
I called to tell them the confusion on my part and that I didn't know this was happening. It didn't matter, they are holding the position that they sent me statements it is on the statements. I asked them to reduce this interest, it wasn't what I had thought I signed up for and they have refused to work with me. I told them they do not even consider the payments I made as I paid nothing back! They tell me their terms is they'll tack on interest from the original purchase price and nothing less. This is outright predatory and abusive!!! Synchrony is taking advantage of consumers and misleading them with the logo of Mattress firm pretending they are that company when in fact they have nothing to do with them. I have been misled and I am asking for no deferred interest and only attach interest to the existing balance at the rate on their statement from the date that the promotion period expired. I will pay interest from there on, but for their false and misleading promotion and advertising I do not believe I should pay for the deferred interest terms they duped me on. From the inception of purchase I was misled.