Courtesy of the mobile and service cost reduced drastically, everyone has more than one mobile and most of the new users don't know how to use the mobiles even, they keep redialing the last call not knowing where they are dialing and how to get rid of this situation...

Further when you say that 3-4 new numbers explains it well...one novice dialed to his contact and found you and he is not sure, he dials again and again finds you....still confused he shares your number with associates mates thinking his mobile is limited version and or has problem to dial wrong connections....eventually all four failed to reach the right guy...this seems unbelievable but it has happened couple of time specially from the delivery people...

However, you are the judge as you established a vocal contact and better know from the tone.
In case your judgment suggests that someone is really bothering you on purpose, you have all the right to register a complain to your local police station.

All the best