Kitchenaid superba stove

We have a Kitchenaid superba stove with a ceramic cooking top. The controls for the stove can be locked by opening the stove door and pressing the numer 3 for several seconds. A short beep and a sign "locked" show the success. To unlock the oven controls you have to us ethe same process. A few days ago I locked the controls (it's annoying when you touch them and some function you didn't want goes on) and now I can't unlock it anymore. Pressing the 3 lets it flicker, but no more activity after that. I hoped the system would reset when I turn the power off, but after 6 hours the problem was still there. (There must be a battery inside, because the clock showed the time when I turned it off). Has anybody any advice on how to reset the stove? Thanks!