How can I return a unwanted item that an ex-fiancee purchased?

I was in a relationship with a woman who was seduced by a salesperson into having her sell Rainbow humidifier/air purifier/vacuums in exchange for one of them as well. The cost was almost $3000, but the salesperson said that she would help my fiancee sell these things in order to pay for the one we purchased. My ex-fiancee made an attempt to sell them, but gave up. The monthly payment is $95, but she said that she would pay half of the monthly payment herself and I would pay the other half. We broke up less than a year later, so now I am stuck making the full monthly payment myself since it was charged on my card. The company who sold it to us refuses to let me return it. I don't need the money I already paid for it back, but I would like to not have to make the monthly payments, since I can't afford it. There is a little over $2000 I still owe, and I don't want to ruin my credit by refusing to make payments.