Suspicious Calls from similar O2 numbers

[Ohtwo]

I have been receiving calls from multiple O2 numbers, all of which the same as mine except for the last 3 digits. I’ve called 2/3 of them back only to find someone just as confused as me at the other end of the line. They all swore that they hadn’t called me and that I had called them, when I didn’t even have my phone in the same room as me. What’s happening?

[MI5]

@Ohtwo 

Scammers spoof numbers into autodiallers and is sadly all too common these days.

Those customers who "called" you never did. It was  scumbag con artist.

[Ohtwo]

What do they gain from doing that?

[MI5]

@Ohtwo 

It makes them impossible to trace.