OP, I don't want to hinder you doing what is the ONLY action open to you which is to complete(including getting your signature witnessed) the PE3 and then send to the Traffic Enforcement Centre.
We give this advice so often that occasionally we might forget an OP's level of knowledge.
Yours is practically zero, c'est la vie.
Therefore matters have to be particularised.
The 'they' in the previous post means the Traffic Enforcement Centre, nothing to do with TfL. So make sure you understand the difference.
The PCN won't be cancelled, it's the Charge Cert and OfR which are. TEC will instruct TfL in whose court the ball will land. If they want to continue then they must refer the matter to the Tribunal(adjudicator) for direction.
But for the moment just complete the PE3, DO NOT SIGN YET, arrange to get your signature witnessed at your local court(free but might be delay) or solicitor(a small fee) at which point you then sign, email to TEC and make sure it's in time.
Is this clear?