I agree this is a breach of etiquette. Some companies encourage such behavior by their employees in a misguided attempt to intill a friend or family type rapport with their clients/customers. Personally I consider it a lowering of the Etiquette Standard. If you find it offensive you may politely tell them you prefer being called Ms/Mrs/Miss Houghton.
We had a sales rep calling on us, who tried to employ this tactic..
"Well, you see, Alex.... may I call you Alex?" and he smiled broadly.
I, smiling equally broadly, replied sweetly,
"No, I hardly know you. You may call me Mrs Price." (I've since divorced, but that's irrelevant....)
He completely lost his way. That reply was so unexpected to him, and he was so totally unprepared, that he proceeded, over the NEXT 4 HOURS (!) to pour his heart and life-story out to me, all his tales of woe and problems, that, well, he basically lost the sale. We never did go for the fully-fitted bathroom he was trying to sell us.