Well, sorry, but looking back through the thread, it is your own fault you are in this situation because you did not submit any representations against the PCN within the 28 days allowed. The council may at their discretion accept late reps, but having now served a Charge Certificate are unwilling to do so, and they are within their legal rights, sorry to have to say it.
So you are now liable for the £105. If no payment is made, the the council will register the debt at the Traffic Enforcement Centre, (TEC), adding £10 onto the £105, and serve an Order for Recovery.