Phone calls about iCloud having suspicious activity

I have been getting phone calls every 5-30 minutes about my iCloud having suspicious activity. It is a recording and sound anything but legitimate but they are persistent and have called 25 times or more. Every phone call has the same first 6 numbers as my number but the last 4 are always different. How can I verify if this is Apple support or just another fraud trying to get information? And if it is fraudulent how can I stop the calls since blocking the number wouldn’t work since it is always a different number?