Contract-Holder Said Was Leaving but Furniture Remains

Hi, We have had tenants in our property for about five months that are still in a fixed term and have caused various issues. 

They have asked to leave early due to financial difficulties, to which we have agreed. I was told there was only a sofa left at the property.  I haven't had contact with them for over a month now, and the rent is overdue by about six weeks. 

I carried out an inspection last week that I gave notice of, and there was more than just a sofa left. I have sent them an email with the list of items and informed them that they are still responsible for the property until the keys have been returned and that they have told us that they have vacated. What are the next steps if we don't hear back from them and they don't empty the property? 

What else do you advise, please?