Vermieter entered my Wohnung without my consent for a Besichtigung

I moved out of my apartment (1000km away! Because of work) but still pay rent for it. I gave a key to my Vermieter saying they can show the apartment to others provided they ask me beforehand. There was no official Abgabeprotokol or an official Schlüsselabgabe. These will be done when my comtract ends. I still have a set of keys as well as right to the apartment until the end of April. My vermieter recently emailed me saying they did a Besichtigung (without my consent) and sent me a whole list of things that are defect in the apartment. As far as I know, they cannot do this without my presence simce the place is still mine and they entered without my consent, plus, brought strangers into my living space without my consent. I am thinking about involving the police. What can I do here?