Conn's Home Plus

I purchased a washer & dryer from Conn's in Hurst, TX. I have paid on time and over the amount. I called in October 2018 & I owed $600.00. I called to pay it off in December 2018- the price had went up to $1400.00. They had lied to me on the phone over the amount and when it was due. How could it jumped that high. I also paid two addition payments of $200.00 total before December 2018. They will not work with me and want the full amount of over $1400.00. This is crazy, they have been rude and every time I call in to them, they tell me something different, I refuse to pay them that much, it's over payment.