You didn't do anything wrong. Phone numbers are recycled so its prior owner could have answered or returned calls and this number gets marked as "live" so the robots all pile in to call you.
If you can't use NOMOROBO and will not install a blocker app or such, then does your carrier allow you to whitelist the numbers you do want to call you?
I Live in Canada. I purchased a Motorola Moto G3 about two years ago. Since then, I have made two trips to Florida and although I never made any calls while in the U.S. I am inundated, almost daily with calls from all over the U.S. Mostly, I don't answer calls from numbers I don't recognize, feeling that a message will be left if it's important, although I did answer two or three and they are telemarketing, robo-calls, or some type of scam. Is there any way to stop/block these calls. Blocking the number isn't an option since there are too many.