what part do i need for my dryer hose?

I have just had a hole put through the wall for my tumble dryer hose the bloke put a white two flap plastic cover on the outside,with nothing else before it.I have started getting mice they are coming from there.I am also getting fluff coming out what can i do to block it off but still use my dryer.how much and where do i buy if there is anything. Thank you