Teens using drugs and leaving litter in the Willowhale car park

These teens park their cars there at night, and leave all their rubbish, can, bottle, mac donalds, and drug cannisters, there most nights. I picked up all there rubbish again early evening around 9pm, and found a load more there this morning. This has been going on for a long time, and i have told them myself not to leave all their rubbish there, but they just laugh and take no notice. It has been reported to the police, who went around their houses (as we had photo's of their registrations, and told them to stop parking there and littering, but they still do it regularly. The pcos' finish working at 10pm, and they are gathering there later than that. There was also human faeces and toilet roll in a slight clearing where they were parked, which is disgusting! There is a camera on the library building, but it is pointing the wrong way, or they could be filmed doing what they are doing, as they always park in the same spot. They are not exactly hiding what they are doing, as they are leaving all there empty gas cannisters, balloons and empty drug packets, for anyone to find.