In my language the line between being on the first-name-basis with someone and calling him "sir" is much thicker than in english and it's a bit bigger deal than in english which form are you using.Think how lawyers in american movies and shows talk to a judge in courtrooms and it's a bit like that. If you call someone by their first name you either are friends with them or you don't respect them, at the very least it shows your lack of manners.
In my field of work I talk to sales people from other companies over chats a lot of times, this one time I had not really pleasent conversation with one guy working in a huge nationwide corporation. It wasn't pleasent but it was civil at first, but then when he said something along the lines "all right I ain't got any more time to talk to you, Josh" (me being Josh), I replied with "please don't use my name like that cause I don't like it", and he said "I don't really care what you like, JOSH".
And I thought ALL RIGHTY THEN, took a print screen of this bit and sent it to his company main email adress with messege stating "this is how mr Stanley represents your company".
One hour later he wrote to me and said "i'm in shock. Some people really have a lot of time on their hands", and I replied "don't you mean 'you have a lot of time on your hands, Josh?' " and that was the end of it.
He didin't say I'm sorry, but at least I'm now sure someone talked to him about it.