Calls are bordering harassment now

Our company cell phone is receiving a number of calls daily from this firm, which is looking for someone who has never worked at our company. I block the number of the call each time, but it looks like they have an infinite number of phone numbers, because the calls do not stop. Most calls do not have anyone on the other end that you can talk to. On the ones that I did manage to talk to someone, I have told them that the person they are looking for has never worked at our company, but that does not stop the calls from coming.