Contacts by booking.com

I have a large turnover of guests by nature of my business. Because booking collect payments I tell guests to contact them for modifications. They seem to have no set way of handling modifications. Sometimes they email saying I can only deal with modifications by email, sometimes they phone. Today I did a modification by Pulse even though the one yesterday could only be dealt with by email. I am writing about the phonecalls.  If somebody calls and says they are from booking and asks for information about my business how am I to know that they are. In this day and age of multiple scams it seems risque to give information by phone. Knowing the system as I do, if I was on holiday and wanted to modify a booking I could easily call the hotel, say I am from booking.com, ask the details of the person who answers and advise them to handle my modification favourably. It sounds far fetched but it also seems lapse security to ask for business details by phone.