You cannot, unless you have power of attorney. He can contact that business and inform them of the problem and have them put a block on his name and number combination such that a person would need to provide positive identification in order to overcome this block.
He could attempt a restraining order for harassment along with cease and desist. Of course, it was likely one of his friends just having a laugh. Let him handle it though. Honestly.
so bad.
Very likely they picked random numbers and didn't mean to use a real one.
Just email them and tell them the mistake, they might change it if you ask.
Someone has used my boyfriends name and number and posted 3 ads on gumtree, how do I get them removed? And would the police do anything? It's ridiculous