Downstairs neighbour left me a threatening note

Hi! I’ve recently moved to a place and I found this note under my door. I live alone and I’m not doing much at night to warrant this tone. I’m going to be more considerate in the future but what can I do? Should I complain to the letting agent? I feel very uncomfortable and threatened.

Hi! I’ve recently moved to a place and I found this note under my door. I live alone and I’m not doing much at night to warrant this tone. I’m going to be more considerate in the future but what can I do? Should I complain to the letting agent? I feel very uncomfortable and threatened.