+1.
There is NOTHING you can do at this stage because that's procedure.
The penalty won't increase*, it will decrease IF you follow procedure which is set out clearly in this link, start at Charge Certificate:
This section explains the enforcement process for a parking Penalty Charge Notice, where the vehicle was not clamped or removed.
There is nothing unusual, rare or unique about your position, we see similar threads regularly. We know the very straightforward procedure and would guide you. Ultimately, your next step is to tick one box on a form, sign and send as directed (email preferably) to the Traffic Enforcement Centre who will CANCEL the charge certificate. The ball would then be in the authority's court.
*- as stated by others, procedurally the authority have to pay TEC £10 to register the debt and this is recoverable from you if you don't follow our guidance. But this and CC surcharge are both cancelled by TEC if you follow procedure.