Can I threaten them with a lawyet on a refund?

To be completely honest, if you to actually get a lawyer you are looking at that $3000 and more, they know that and know that you would not do it. Plus they are illegal, tribal or offshore lenders that the lawyers would not waste their time with. Technically you signed a contract with them, that stated you would pay all the interest. It was illegal for them to lend you the money, but you went looking for it. It was not forced on you. I like you have a lot of interest paid. I did the math and on 1 loan company only, since 2009 I have paid over $6K interest only. I have loaned 4 times with them, but paid over $6k in interest alone. Honestly, at this point I am glad they just accepted my offer to go away and leave me alone. Or else I would of been paying them another $2300 in interest. I would just call it an expensive lesson. You wont get any money back and you are just going to stress yourself out.