Unfortunately, it is quite common for new owners to holiday parks to make unpleasant changes to the terms and conditions (the most usual one is deciding on a new van-age limit, meaning that a lot of owners get told they have to upgrade or vacate). A site maintenance fee in addition to a pitch fee is not so unusual with some of the new breed of operators.
If your existing contract is still within date, you can try arguing that the new owners should honour existing terms until the contract expiry date, but if they refuse there is unlikely to be much you can do about it.
Has the new owner issued a new contract? Are the other terms acceptable?
It could be worthwhile contacting the local council to make sure that the new owners have correctly applied for the site licence to be transferred to them - if they have not done this, then they may not have the legal right to collect any money from you.
Has the park actually been sold? or is it the same owners rebranding themselves as a new company? (have a look on Companies House webcheck to see if the company directors are the same in both companies).
If either are the case (no transfer of site licence, or the same company under a different name) it could be worthwhile contacting Trading Standards, or maybe your static insurance ha a legal helpline?
Whether or not this is something you want to pursue is, of course, something only you can decide; it may be that their are improvements in the pipeline that will make things better for you, and the new owner has to raise some money to pay for them.
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