Hello again Minikar.
I think its twice you have quoted site owner "Changing the fuse". If he is relying on fuses, then his wiring is well out of date. He should be using Miniature Circuit Breakers (MCB's) to provide overcurrent protection, and these only have to be switched back on - no fuse to be replaced. If the sites systems have started to melt, then that is fault with the sites systems, regardless whether you did or did not exceed the Ampere rating for your pitch, the bollard should have protected itself by isolating the the supply.
I must add, I'm not advocating carelessness with electrical loads, You should always be aware of any power limitations a site may have therefore select what appliances you use to keep within the supplies limits. But the MCB's are there to protect and isolate cables and switchgear from inadvertent excessive loads.
I hope the situation can remain amicable, but the more I read about your experience the more concerned I become:- Its beginning to sound as though the site owner is trying to frighten you into agreeing to pay to repair a system which should have protected itself. If it has failed to protect itself, then it is inherently faulty and it is hazardous a fact proven by the melting of some components. That is an offence under the Health and Safety and Electricity at Work Regulations. The owner of the equipment is legally responsible for its safe and correct operation It must not present a hazard to anyone that uses it.
My advice is if the site owner attempts to try and charge you extra or for repairs, consider refusing to pay the extra.
You could try calling the site owners bluff, and blame him for directing you to connect your caravan to an unsafe supply about which you are seeking legal advice.