Police say or Police says

In one of my classes, I was asked why 'police say' is used instead of 'police says'. Is it a mistake? Is it really a mistake? While 20 years ago the word 'police' was perceived as a singular noun, resulting in the verb taking the -s ending – 'police says' – nowadays 'police' is perceived as a plural noun because it refers to multiple people, so the verb does not take the -s ending – 'police say'. Language is a system that continuously evolves, and the example mentioned above shows how exactly this happens.