On what planet do you imagine "paying them off" is a better option than owing them zero? You don't owe an unregulated private parking company a penny. Of course you fight this, all the way to court if necessary.
To start with, please make sure you've read this thread:
READ THIS FIRST - Private Parking Charges Forum guideShow us one of the NtKs (both sides) you received, suitably redacted of personal details, VRM and PCN number, leaving all dates visible.
Are you a leaseholder or a tenant? Either way, what does your lease/AST say about parking? What it doesn't say is equally important. For example, is there any mention of a requirement to display a permit? Is there any mention of any liability to a third party for spurious or speculative invoices for breaching any parking regulations?
It is highly likely that your lease/AST has supremacy of contract over anything that the managing agents decide to impose on you, such as an unregulated private parking company who are taking the liberty of charging you £100 per day for parking in your own demised parking space.
Please answer the questions about the lease and what it says and doesn't say about parking or quiet enjoyment and so on.
