Payday Loan Co. Breached the contract

I have a different situation i think. I have a loan with MyNextPayCheck. I have been dealing with them (use to have other names) for about three years. I have to say they have been very helpful as far as when i needed a quick short term loan. I always borrow and pay off the balance on my very next pay date. This last time i borrowed $350. The pay off is $455. I'm not complaining about that, i know this is the route you have to take when you have messed up credit. Ok my loan agreement is to have my first payment taken out of my account on 8/3/2012. They went into my account on 7/26/2012 for the payment. (8 days too early). Of Course i didn't have the money and was charged a $35 NSF. I contacted them and they confirmed that the error was on their part, someone set my account up incorrectly and put the wrong renwal/payoff date in the system. They said that my account will automatically go to collections but there is a note in my account that their system debited my account to early in error. They informed me that if i send something from the bank showing that i received an NSF from the error it will be reimbursed. When i log into my account on line they still have the dates set up incorrectly. They don't match the dates on my payment plan on my loan agreement. I told them about this and they said they are aware that the dates are set up wrong and they will correct them. They haven't corrected them yet. I contacted my bank and placed a debit hold and a ACH block on my account, since they still have the ACH dates wrong in their system. I sent then an ACH Revocation later since my loan agreement says that we can choose to pay by money order. I also filed a complaint with the Tennessee Attorney General and the FTC just to cover my butt if they try to act stupid when they finally call. Now what I'm thinking is that they are in breach of contract. legal cause of action in which a binding agreement or bargained-for exchange is not honored by one or more of the parties to the contract by non-performance or interference with the other party's performance. If the party does not fulfill his contractual promise, or has given information to the other party that he will not perform his duty as mentioned in the contract or if by his action and conduct he seems to be unable to perform the contract, he is said to breach the contract. Now if they are in breach of contract i feel that i no longer owe the interest but only the principle less the NSF charge that i occurred due to their system debiting my account to early in error. Their collection dept have not contacted me yet as this all only occurred 3 days ago. When they call i want to pay only the $350 principle less the $35 NSF which in turns come out to $315. Am I in my legal right to request that. Please note that I am not trying to not pay anything I just feel that since they breached the contract that erases the interest and leaves only the principle less the NSF fee that I owe them.