This reminds me of a conversation I had with a women when I worked in banking.
Customer: I have a 50,000 line of credit. I keep paying $200/month towards it, and this statement says I owe $51,000! How?
Me: Well it looks like you selected the interest only payment option[not even bringing up the fact she missed a couple payments.]
Customer: I have been paying on this thing for 10 years[actually 8]! How do I owe more than I started with[she is just NOW realizing the balance didn't go down over 8 years].
Me: Well the interest is about $198 a month so if you are only paying $200 you aren't paying against the balance, just the interest. If you wanted to pay it down over 10 years the payment would be around $500 a month.
Customer: I can't afford that!!!
Me: [having looked at more numbers] You aren't going to like this, but I want to make sure you are aware well in advance. In 2 years the repayment period starts and your payment will probably go up to around $330 regardless.*
Customer: [It was scary.]
*That is how a lot of HELOCs work. You get 10 years where you can draw against it, and then a repayment period of either 10 or 20 years starts. Most people just refinance into a new one if they plan to keep using it, but it gives the bank a chance to review the situation every decade instead of giving you a loan for infinity.
This is actually starting to be a problem now. There are a few articles on it. A lot of people who got HELOCs in 2005/2006 are about to enter the repayment period. Those HELOCs were issued at the peak of the housing market and some of these people are 'still' underwater so the refinances aren't going through so the people are seeing their monthly bills shoot up hundreds of dollars.
http://blogs.wsj.com/totalreturn/2015/06/08/if-your-heloc-payment-is-about-to-jump/