The Callers ID can be amended to any number wanted. It can be done so that you call back on a free, 0800 number rather than the real number used.
That means, of course, it could appear to be from anyone or any business the callers want you to believe.
If I don't recognise a number, I ignore it and check it on the internet if need be. If they really want to speak to me they will leave a message.
There are various dialling codes that cost a fortune to call so the last thing to do is call a strange-looking number before checking the rates.