This is a pretty common scheme. It certainly doesn't sound very fair, but as long as they laid out the terms, you have to abide by them.
You do still have some . This is a lot of money and a long term contract you are talking about - 2 years at a time. I would not give up so quickly. No company wants to be in litigation, so the threat of litigation can be quite powerful.
Start off with a letter to them in writing sent by registered mail, demanding that they cancel your contract and refund your money. Explain that their auto renewal was not make clear and obvious to you, that it was on the back of the agreement, and that you no longer require their services. Be clear, concise and non confrontational. It doesn't hurt to mention at the end that you are prepared to follow your legal recourses.
This will start a paper trail. Hopefully they will respond also in writing. Don't take any more phone calls, you want it all written down.
Keep on them, if you have a couple letters back and forth with no movement, start having an attorney send letters (you can even just ask a friend rather than hire someone).
If that doesn't work, bring them to court. Most cases settle just based on the threat of a court case. If not, go to the judge and tell him that this was an unfair trade practice and see what you can get out of it. There is no guarantee, but it's worth a shot if you don't have to spend to much money to litigate.
I hope this was helpful ad good luck.