Entry after move out date

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I wonder if anyone can advise where I stand please.
I’ve had a tenant for two years. He’s never around when I go to the property to clean the communal areas but his adult step son and girlfriend are always there.
The tenant gave notice via email and I responded to accept the notice and confirm the tenancy end date.
We are now 5 days from the end date and the tenant nor the stepson are communicating. I have emailed regarding move out procedure and asking them to arrange a mutually convenient day and time but no reply. I can see that my messages and emails have been read and ignored. There doesn’t appear to be any reason for this and I’m totally confused as to what’s going on. I did receive a text from the tenants partner yesterday (she has never lived at the property) saying I am harassing the tenant by sending a text and an email and he is very busy at work. She hinted that the step son might not have anywhere to go to and promised to get the tenant to ring me last night but as suspected, no phone call came.
I put some paper under the door of the flat a week ago and it hasn’t moved so I’m unsure if anybody is actually there. It is an upstairs flat so I can’t see inside.
If I get no response from my messages to the tenant, can I just go in on the tenancy end date and take possession on the basis it’s all been agreed on the email ?
Is there something potentially going on here that I’ve missed ?
Any advice appreciated.