On 5/17/17 I got a call from "Upper Marlboro, MD" from this number, and they did not leave a message. I don't answer calls that don't show up on my caller ID, thinking they are scammers when they don't leave a message, and I always block them.
You should realize this has NOTHING to do with the cell phone companies. Phone numbers are not secret by any means. Anyone can pickup a phone and dial 10 random digits. These scammers have autodialer machines pumping through numbers all day. With multiple scammers out there, it is no surprise our numbers get hit over and over again. Need government to crack down harder. Ultimately though, we need a more secure / more advanced method of protecting phone numbers. They system is just broken.
Another car warranty scam. I have signed up for do not call lists (state and federal) but these numbers keep changing, I keep adding numbers to the block list, and then a different number calls with the same pitch. I think it's time for me to actually find out the actual company so I can file specific complaints about it.
Just know that they're not legitimate calls. The people who are making them are operating illegally and don't care whether or not you're on the Do Not Call list. As far as I know, the best thing you can do is to never answer calls from numbers you don't recognize and to be careful with who you give your number to. If you answer, they will know that your number is valid and will start calling more frequently.