Rent not paid for a year +

Since feb 2019, I have not received part of december 2018's rental, as well as last 12 months rent. Their front office carry on like nothing is happening to this place. They used to run a decent rental company. Now I think one of their staff is staying at my flat basically less than my rates and taxes money, and levies. And hasnt paid a cent. 4k electricity not paid. Sad. Im busy calling my lawyer to sort them out.