Some things can be taken away and there is no compensation or notice needed- eg we used to get a free daily paper and free water. But something like a parking permit that was mentioned in your offer letter is significant enough to require, as eddie says, notice as per your contract. I think it can be up to 3 months rather than 6, but can be less. 4 days seems too low.
As for compensation there is no entitlement provided they give notice. Sometimes a change like this is rolled in with other changes and the company argues the effect is broadly neutral across the workforce so no specific compensation is given