Contract law is a powerful force. It permeates throughout all law. Courts will not interfere with contract law unless the contract was due to 1) mutual mistake 2) there is no consideration 3) no legal capacity 4) no requisite capacity 5) violates public policy or laws in the state 6) contracts for an illegal act. When dealing with big companies, it is typically hard to meet any of the issues in 1-6 (not always, but most of the time). These bigger companies usually have a legal department that makes sure their contracts are sound (again, not always, there are lazy and tired attorneys out there).
If the contract is valid, in California, it is fair for a collection company to collect interest and fees, as long as you agreed to it in your contract. California Consumer Affairs, and read Article 2.6 paragraph #2. So the real answer is -look at your original contract. This would not be the paperwork by the collection company. This would be the paperwork that underlies the debt.
Thankfully, under bankruptcy law, most unsecured debts are dischargeable. If the collection company is harassing you, and you are foreseeably unable to pay the debt, give my office a call. We will help.