Found this from a google search ("scam calls coming from last 3 digits of my number changed").
I'm an O2 customer and been getting these a lot. I've installed an app that came recommended called "Mr. Number" from the Play store, that lets you block all numbers from a range (except any in your contact list), so it now auto blocks anything that is almost entirely the same number as mine except the final 3 digits, which solved it.
Nobody has stolen your number. Nobody has stolen your phone. And there is ZERO point in reporting the numbers to any system as the numbers are spoofed.
Spoofing happens because call centres (usually Indian based) used VOIP (voice over IP) - a system that lets them use the internet, to call people on phones, automatically. To do this, the receiving end needs to be told a phone number (even though the origin is actually an internet IP), and lets them literally enter any number they want. There is no verification. No security. No check. They can make it look like they are calling you from your own number, your parents (if they happened to know it), even your local bank branch number or your doctor's GP number.
The entire system is broken, and needs fixing at a fundamental infratstructure level. Phone companies in the UK need to come together and push for a fix - NOBODY should be able to call from abroad and be able to input any single number they want to appear at the recipient's end with zero checks security or systems in place to prevent it.
It's ridiculous that the entire phone network allows this.
