They didn't "get" your particular phone number from anywhere except a sequential dialing program. It starts out with all valid area codes, then it's easy to plug in the various phone number extensions (1st 3 numbers after the area code) and then it just started at the beginning of all possible 4 digit number combinations - 0001, 0002, 0003, 0004, etc., ad infinitum. The computer can dial more than one number at a time, and if there's someone there available (not trying to scam someone else) then it captures your phone number if and when you answer, and you get connected with the next available, aspiring crook. Your number probably gets put on a list of legitimate phone numbers for sale to someone else to use for the same purpose.
Best thing is do not answer phone numbers you do not recognize, because if it's legitimate they'll leave a message, and if they don't, then it wasn't very important to begin with, or just a scam like this one is.
Find out if your State Attorney General's office or similar agency in the state government, deals with telephone fraud, especially this kind of fraud, and has s system to report them. The FTC and the FBI and other national government offices also have a way to report fraud, such as the one that's been going around with people impersonating the IRS! If you don't report it, and everyone else thinks their one and only report won't matter or help, then nobody reports it. And without reports, from EVERYONE, then how do the legal agencies proceed to put a stop to it?
Yelling you want them to "STOP CALLING ME!" here isn't the answer, because nobody here can help you make that happen. Just wondering how they just happened to get your particular number is a legitimate question, but finding out the answer won't really solve the problem either. You've got to take it a couple of steps higher and REPORT IT to the people who can do something about it. They have the resources to help you and the rest of us.
There are many who have already been found, prosecuted for all the charges that can be put on them, and had heavy fines levied on the lot of them, where some do get jail time as well. And several of them were running what they called the "Rachel scheme" with the female recorded voice that tells you they can help lower your interest rates on your credit cards, and dial 9 if you want to speak with a person.
My State Attorney General's Office fraud repottirng staff and I are all on a first name basis because I report every single one of these I get!!! And I frequently receive real mail responses to my reports. But they can't do much of anything with just one person's report!
So, REPORT, REPORT, REPORT!! That's the only thing that will stop these people!