Thank you. There is unfortunately no quick fix to this. Your options are really twofold - the police or the courts. With the police, you have to report this to them and then it is in their hands. How soon they deal with it will depend on the nature of their actions, the severity and seriousness and how likely is it that it may cause immediate harm. But you cannot force the police to act quicker than they decide - it is all down to them.
The other option is the courts, where you can get an injunction for example. But that will also take time, a few days usually for an urgent injunction. In the end all it gives you is a piece of paper which says what the person cannot do, such as contact you. It still relies on that person following that order but some people will just ignore them. If they do ignore it and continue harassing you, then the police can potentially get involved again.
In order to keep costs down I would strongly suggest you stick with the police here - the court option will be expensive and still no guarantee to putting an end to this. I would say you should press the police to deal with it quicker, perhaps by highlighting any serious behaviour by that person, which indicates they may expose you to further harm, usually physical harm.
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