We had the same issue at our rental and it was awful. We've moved now and I didn't know what to do so we dwelt ith it ourselves but someone recently told me that if the mice can get in from outside ie, holes in house from bring old etc. it's the landlords issue not tenants. If its a new place and its not easy for the mice to get in from outside then it's tenant issue. I would be calling your agent and advising them that something needs to be done and soon, especially as it sounds like a health hazard.