The amount can only now increase by £10, which is the fee for registering the debt at the Traffic Enforcement Centre, (TEC) at Northampton. When CoL does this, they must send you an Order for Recovery, and also include the form to submit a Statutory Declaration to TEC that you never received the original PCN. You fill in the form (PE3), get it witnessed, (free at councty court, or circa £10 at a solicitors), and send it off. It's best to send it off electronically if you can.
TEC will order the CC and OfR to be cancelled, and you return to the PCN stage, at which point you can pay or appeal.