Millie
Hope you are ok?
Ok, Lock your door and don't open it particularly as you are on your own.
Call the police if you need too.
You need to get yourself to the CAB or a solicitos.
Are you renting or did you buy the flat?
If your renting contact the owner or the company and ask for their help. They should be able to supply you with a ref and contract from when you moved in.
If you are buying you already have this info but your solicitor will suppy you with a copy.
Are you on the electorol role? Contact the local council and check that the last occupier is not!
Next countact your local court and check that there is not a CCJ against the other person at your property.
Do Not be intimidated! YOu are not a bad person you have done nothing wrong. Lock your door and call the police or a neighborough or friend to explain to the baliffs out side do not let them in.
Where in uk are you?
I have a friend that is a baliff and I will check that there is nothing more you can do tonight.
Hope you are ok.
xx