What is the exact message you are seeing?
If you are seeing that ' someone' is using your account from a different location to that where you are located, we all get this from time to time.
As long as your log in time is correct the same for when you are logging in, then all is well.
I live on the South Coast and often receive a message that I'm logging in from Birmingham, but the log in time is correct the same as my log in time, so there is no issue here.
If the above is not the issue you've encountered, then you will have to report your account to Customer Services here:
https://www.ebay.co.uk/help/eua?id=5275&mkevt=1&mkpid
@fernwoodboy1