At this point I would just ignore them.
The 'reasonable assumption that you were the driver' argument went out with flared trousers but they continue to spout this nonsense because there is no other option available to them.
These charges are virtually unenforceable in my opinion and pretty much every case gets defeated in Court when properly defended.
Come back for more advice when you receive a Letter Before Claim.
There will be begging debt letters but these are utterly powerless and meant to frighten people into paying.
VCS and Excel are the same company and, once again, they suffered another humiliating defeat in Court when a totally unqualified member of the public stood up to them and defender her corner - read about it here;
https://www.thestar.co.uk/business/excel-parking-court-defeat-8753941
