L.,
You might want to take a look at Colorado's fair credit Act. A company cannot change your interest rate or loan, even if they sell it to another company without your consent or approval.
1. Request that the company send you all of their documentation, there are websites that teach you how to write up your response.
2. Make sure they know that you know the law.
3. Don't be afraid of them. If they are attempting to change your interest rate or loan you can sue them, that take money on your part, but if you put as much of their business out there and have the documentation to prove it, that works in your favor.
4. Be persistent and save every single bit of information that you get from them. File it, and tuck it away.
5. Try to get out of the loan as quickly as possible by paying down the principle on the loan. To do that, you simply sind in payments between your regularly scheduled payments with a note in the sideline that says that it is to be taken from the principle and not the interest. If in your next statement the company did not comply with your wishes then that is one more thing you can put before a judge.
6. Here is a url that might be of assistance in dealing corrupt lending practices: http://www.hud.gov/local/co/homeownership/predatorylendin...
I am sure that this sounds like a lot of work, but the main thing is that, you should not have to pay more then you agreed to pay for this house, the company has no right to alter your terms, and the only defense against such a huge company is to go after them with their own information.
Who knows you might just take them to court, force them to pay your fees and get the judge to get them off your back once and for all. However, if you are not willing to go to court, do your best to get out of the debt by paying it off as soon as you can.
I pray this has been helpful to you.