I’ve tried to upload the claim form but it won’t allow it.

I’ve just received a Claim Form from the County Court regarding a PCN issued originally in July 2019 by DCB Legal Ltd. The PCN was issued because I was parked on private land ie. Urban Exchange, Manchester. The claimant is Highview Parking Limited. I admit I overstayed the 1 hour 30 minutes limit by 20 minutes but I refused to pay, primarily because I thought the charge was excessive and more so because I decided that trying to reason with these charlatans would be completely futile. At no stage have I ever admitted guilt or even entered any kind of dialogue but I admit now we have reached the 11th hour, I am completely out of my depth and facing a near £300 charge Any advice would be greatly appreciated.