I thought that for a while as well, but having done a bunch of photo assisting recently on the side of my video stuff I've gained another perspective on it. Basically, they only "own" the photo as long as the rights specify. So technically they only "owned" the rights for that 10-11 season as specified, and any use thereafter is a breach in the contract. The easiest way to make things right is, like someone said above, simply send over an invoice in an email along with an explanation and a copy of the last rights agreement. Be understanding yet firm, as some people just don't get the concept of a rights agreement.
It seems like a pretty simple mistake, and I'm sure it was, especially if there were all new people dealing with the photo. However, it's important that you stay on top of your rights agreements and pursue this. Also, looking forward, instead of saying '10-11 or 11-12 season', it might be best to go by year(s) from the shoot so there's always a date set in stone for when that license is no longer valid. Best of luck in getting this figured out.