OT: Annoying spammers

Some idiots have taken our companies phone number, inserted it into their caller-id bits (seemingly with SIP phones), and have been harassing people.
So we get frustrated people calling us, asking us if we called them.
No we didn’t. I hate phone marketeers as much as everyone.
This is really annoying. Can’t see any rational reason for this other than someone trying to steal the companies reputation.