impertinent letting agents

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I was appraoched by a letting agent in South East London recently in response to a letting advert in Gumtree. The caller said he was a partner in the agency and was himself a professional landlord. He asked me if he could be given a chance to find suitable tenants for me . I insisted that I needed to see his office and interview the tenants myself in person . I made an appointment to go and see him . When I arrived he was not there and phoned to cite a health problem and asked me to speak to his colleague which I did. I also talked to the tenants they were recommending . It appeared that the letting agency had not obtained all the information about the tenants and basically they were not suitable tenants for my property.
I called the letting agent and left him a message that the tenants were not suitable and declined their offer. Later that day the agent called my mobile and left an abusive message on my mobile containing a lot of swear words.
I called his partner and complained and asked for a written apology which I have not yet received.I found this unacceptable and would like to know where or which agency I can complain to
Please advise if I am at liberty to name and shame this letting agency on this forum for the benefit of other landlords who may have dealings with this agency.