We had a similar problem with a swing park and grassed area including an “aesthetic mound” created opposite our house. Then Yobs started taking over, destroying the equipment and intimidating other users. Our complaints got nowhere initially until a very strong willed Eastern European lady took us in hand. She told us to keep a detailed log then send it with a short and precise accompanying letter to anyone with the slightest connection, copying them all in so they are aware that others know of their action or lack of action. Local police, senior police, mayor, individual council committees such as leisure services, MPs, PM and ministers, council departments, local newspapers, Uncle Tom Cobley and all! Encourage others to write individual letters as some authorities act only when a certain number of complaints are received. Once a newly appointed police inspector started phoning around (having rescued our correspondence from a bin) and suddenly all the others jumped on board as well. Took a few meetings but eventually higher railings were installed, prickly bushes planted all along the edges, the beat bobby included it on his rounds and the gates were locked every evening and finally peace was restored! The more people you involve the better chance that at least one of them will decide to help out and start the ball rolling. Of course you could just put your property on the market and move on!