VIP Loan Shop Changed Renewal Fee Without Notice!!!

[COLOR=#333333]I got a $300 payday loan back in October which had a service fee of $90. I get paid once a month at the end of the month, and I opted to pay the $90 until I was able to pay off the loan. They debited my account in October and November for $90 so of course that is what I was expecting for December. Much to my surprise they took out $135 in December. I called to inquire about this change and after being placed on hold for what seemed like forever I was then told that a mistake was made and the fee should have been $135 instead of the $90 that I had already paid twice. I asked to speak with a manager, and he was very nonchalant about it all. He reiterated that it should have been $135 from the start and that there was nothing that they could do about it. I told him that the agreement that I signed said $90/month and that is what they had already taken out twice so how could they just up and change it without any notification. He gave me a bunch of bs about how that is the fee when you're paid monthly, but my point is that it is not my fault that someone on their end made a mistake and I should have to pay for it. [/COLOR]

Is there anything that I can do in this situation? My agreement plainly says $90/month and that is what they took out of my account for 2 months straight. If it was going to change the least they should have done was contact me to notify me so that I could be prepared! Luckily I had enough in my account to cover it, but it could have really wreaked havoc on my account if I didn't.