You can return the items via the Post Office or give them to the courier, or keep them/donate them to charity etc.
Some overseas business sellers use randomly chosen UK addresses when they have to provide labels for returned items. This is not actually allowed and you can report the business - google for details.
Unless they are definitely returns, it could also be a 'brushing scam' which seems to have come back.
"There are two ways to be fooled. One is to believe what isn't true; the other is to refuse to believe what is true.”
Søren Kierkegaard, Danish philosopher (1813 - 1855)
