Just stop paying them. In fact, the debtor is in control of the situation. They can dictate whether or not the creditor made a good investment or a bad one.
Let them know that you can turn their investment into a loss if they decide to be assholes and that you don't really care if your credit score takes a hit.
Don't be angry at all about it, just be matter-of-fact.
They are used to getting angry calls, they aren't used to people being very reasonable while telling them what is going to happen if they don't comply.
They don't want to lose money and you are offering them a chance to not lose money.
If they refuse, then make sure they lose money. Call back a few times to see if they are happy with their decision to lose money.
When the bill collectors call, talk to them. Let them know how happy you are with the new arrangement the bank has chosen (which is you not paying the new higher interest rate) and that it has been a boon to your savings. Thank them for their considerate offer. Then try to engage the bill collector in idle chit chat.
They'll think you are nuts. Which at least offers you the chance to have fun while screwing them.