Acima Charging me quadruple for what i purchased Utah

I went into a local mattress/bedding store. My total account amount was 700.00 to be financed, they kindly tell you you have 90 days same as cash. Never do they explain if you do not pay off in 90 days they are totally going to rob you blind. Being on disability, I have a low income. I purchased this in Oct, 2017 after making nearly 150$ payments monthly drafted out of my bank each month they just told me my balance is well over 900$, I really want to file a class action law suit. This is in no way is morally acceptable.can you help me?