pokecenter: You are free to disconnect at any time, without penalty, and any remaining installments would be billed to your final account in a lumps sum.
You must have missed this, yes they put you on 24 month interest free, with no extra costs, but you can disconnect and pay out the remaining on the final bill, try and take a deep breath there, is it the end of the world that they are putting you on 24 months interest free?