Had a similar issue years back, it was underground parking for a city centre apartment but, we were told, people who had moved apparently still had fobs to get in to park so would use it for free city centre parking at times, it was different vehicles, or they'd park in someone else's space which meant that space owner would park in someone else's etc... We ended up getting one of those tall bollards which you can unlock to fold it down get in to the space and had no issues after that.