Who let them into the building? I would talk to SMT about that. In terms of calling the police - that was the correct and proper thing to do. Have they been back in touch to let you know what is happening? You should also get support from your union and ensure that council education leaders know about this. Working as a teacher is now a very unsafe job (just look at my story!) - your darned if you do, darned if you don't or even just darned if someone decides they don't like you. In terms of your anxiety, call the Teacher Support Line (google it). They are amazing and do nothing but listen and offer support.