I read something on CA law that stated that you could begin with traps and do this yourself. In doing so you need to evaluate the size of the problem. If it warrents an exterminator then you should hire one.
So I would immediatly give them 24 hour notice that you are coming in to evaluate the situation. In doing so do a walk through to see if they are creating a mouse friendly home. Either way set traps. Then give them notice when you leave that you will be back tomarrow to check the traps and take it from there.
If you find cheerios behind the stove or fridgerator and under the counter I would have a notice ready to warn them regarding keeping the property clean and sanitary. At that point you need to go back in 3 days to see if they cleaned up the mess. Give them notice :)
Do all this immediatly, today, starting with issuing a 24 hour notice to go in tomarrow. On February 2nd if you do not have rent post a pay or quite. Meanwhile continue doing your job in evaluating how and why the mice are living in the house.